It is true that under different circumstances laws may change. However, why some were changed (as in unplanned loss of "coercive power") as well as the kind of interpretations made of some, can presents a strong case for inconsistencies and some apparent contradictions.
Note that in the following modern teaching is followed by those from the past, and that I do not claim that are all what Rome asserts are "infallible teachings" (incapable of being in error) and there is some disagreement among Catholics as to what class of magisterial teaching some fall into (and thus what level of assent is required, which a Catholic has a right to know), as there is no infallible list of all infallible teachings.
►Present:
►Past:
• Pope Leo XIII, Satis Cognitum (# 9): "The practice of the Church has always been the same, as is shown by the unanimous teaching of the Fathers, who were wont to hold as outside Catholic communion, and alien to the Church, whoever would recede in the least degree from any point of doctrine proposed by her authoritative Magisterium." Satis Cognitum (# 9): June 29, 1896: http://www.vatican.va/holy_father/leo_xiii/encyclicals/documents/hf_l-xiii_enc_29061896_satis-cognitum_en.html
• Pope Innocent III and Lateran Council IV: "One indeed is the universal Church of the faithful, outside which no one at all is saved, in which the priest himself is the sacrifice, Jesus Christ, whose body and blood are truly contained in the sacrament of the altar under the species of bread and wine; the bread (changed) into His body by the divine power of transubstantiation, and the wine into the blood, so that to accomplish the mystery of unity we ourselves receive from His (nature) what He Himself received from ours." — Pope Innocent III and Lateran Council IV (A.D. 1215) [considered infallible by some]
• Pius 9, Quanto Conficiamur Moerore: “Also well known is the Catholic teaching that no one can be saved outside the Catholic Church. Eternal salvation cannot be obtained by those who oppose the authority and statements of the same Church and are stubbornly separated from the unity of the Church and also from the successor of Peter, the Roman Pontiff..” - http://www.papalencyclicals.net/Pius09/p9quanto.htm
• St. Ambrose, "Expl. of Luke: "The Lord severed the Jewish people from His kingdom, and heretics and schismatics are also severed from the kingdom of God and from the Church. Our Lord makes it perfectly clear that every assembly of heretics and schismatics belongs not to God, but to the unclean spirit." — St. Ambrose, "Expl. of Luke", ch.7, 91-95; PL 15; SS, vol. II, p. 85, (quoted in The Apostolic Digest, by Michael Malone, Book 4: "The Book of Christians", Chapter 2: "Those Who Reject Christ's Church are Anti-Christian"). http://www.geocities.com/Athens/Troy/6480/catholics/apostolic4chp2.html
►Present:
• Lumen Gentium 16: “The Moslems together with us adore the one merciful God.” (http://www.vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_const_19641121_lumen-gentium_en.html)
• CCC: 847 This affirmation is not aimed at those who, through no fault of their own, do not know Christ and his Church: Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience – those too may achieve eternal salvation.[337]
►Past:
• Pope Eugene IV and the Council of Florence: "The sacrosanct Roman Church...firmly believes, professes, and proclaims that..not only pagans, but also Jews and heretics and schismatics cannot become participants in eternal life but will depart into everlasting fire.— Pope Eugene IV and the Council of Florence (Seventeenth Ecumenical Council), Cantate Domino, Bull promulgated on February 4, 1441 (Florentine style), [considered infallible by some]
• Pope Gregory "the Great:" The Holy Catholic Church teaches that God cannot be adored except within her fold; she affirms that all those who are separated from her will not be saved. (Pope St. Gregory the Great, “Moralia,” XIV:5)
• Pope Pius IX: Error Condemned: Man may, in the observance of any religion whatever, find the way of eternal salvation, and arrive at eternal salvation. -- Encyclical "Qui pluribus," Nov. 9, 1846. (Pope Pius IX, “Syllabus of Modern Errors;http://www.papalencyclicals.net/Pius09/p9syll.htm)
Contra 3
►Present:
• Nostra Aetate: Indeed, the Church deplores all hatreds, persecutions, displays of anti-semitism levelled at any time or from any source against the Jews (Declaration on the Relation of the Church to Non-Christian Religions, “Nostra Aetate,” Oct. 28, 1965)
►Past:
• Nostra Aetate: Therefore, the Church reproves as foreign to the mind of Christ any discrimination against people or any harrassment on the basis of race, color, condition in life, or religion. (Declaration on the Relation of the Church to Non-Christian Religions, “Nostra Aetate,” Oct. 28, 1965)
• Pope Gregory XVI: It is insanity to believe that liberty of conscience and liberty of worship are the inalienable rights of every citizen. From this stinking fountain of Indifferentism flows the erroneous and absurd opinion, or rather derangement, that liberty of conscience must be asserted and vindicated for everyone. This most pestilential error opens the door to the complete and immoderate liberty of opinions which works such widespread harm both in Church and State. (Pope Gregory XVI, “Mirari Vos,” August 15,1832)
• Pope Pius IX, Error Condemned: Every man is free to embrace and to profess that religion which, led by the light of reason, he shall consider to true. -- Allocution "Maxima quidem," June 9, 1862; Damnatio "Multiplices inter," June 10, 1851. (Ven. Pope Pius IX, “Syllabus of Modern Errors,”December 8, 1864; http://www.papalencyclicals.net/Pius09/p9syll.htm)
• Dignitatis Humanae: If special civil recognition is given to one religious community in the constitutional organization of the State, the right of all citizens and religious communities to religious freedom must be recognized and respected.
• Pope Pius IX, The Syllabus (of Errors):
[It is error to believe that] Hence it has been wisely decided by law, in some Catholic countries, that persons coming to reside therein shall enjoy the public exercise of their own peculiar worship.” (Section X, Errors Having Reference to Modern Liberalism, #78. http://www.ewtn.com/library/PAPALDOC/P9SYLL.HTM)
• Dignitatis Humanae: It is fully in accordance with the nature of Faith that in religious matters every form of coercion by men should be excluded.
• CCC 2298: In times past, cruel practices were commonly used by legitimate governments to maintain law and order, often without protest from the Pastors of the Church, who themselves adopted in their own tribunals the prescriptions of Roman law concerning torture. Regrettable as these facts are, the Church always taught the duty of clemency and mercy [Islam can say the same, but in both cases the religious use of sword of man is sanctioned]. She forbade clerics to shed blood [by having the state do it]. In recent times [like the New Testament] it has become evident that these cruel practices were neither necessary for public order, nor in conformity with the legitimate rights of the human person. On the contrary, these practices led to ones even more degrading. It is necessary to work for their abolition. We must pray for the victims and their tormentors [Rome being one of the latter].
• Pope Leo X: That it is against the will of the Spirit to burn heretics at the stake is condemned as false. (Pope Leo X, “Exsurge Domino,” 1520)
• Pope Innocent IV, Ad extirpanda: The head of state or ruler must force all the heretics whom he has in custody,{8} provided he does so without killing them or breaking their arms or legs,as actual robbers and murderers of souls and thieves of the sacraments of God and Christian faith, to confess their errors and accuse other heretics whom they know, and specify their motives, {9} and those whom they have seduced, and those who have lodged them and defended them,as thieves and robbers of material goods are made to accuse their accomplices and confess the crimes they have committed.
Those convicted of heresy by the aforesaid Diocesan Bishop,surrogate or inquisitors, shall be taken in shackles to the head of state or ruler or his special representative, instantly,or at least within five days, and the latter shall apply the regulations promulgated against such persons [burn them alive]...(http://userwww.sfsu.edu/%7Edraker/history/Ad_Extirpanda.html; http://www.documentacatholicaomnia.eu/01p/1252-05-15,_SS_Innocentius_IV,_Bulla_%27Ad_Extirpanda%27,_EN.pdf)
- • Pope Innocent, in his instruction for the guidance of the Inquisition in Tuscany and Lombardy, ordered the civil magistrates to extort from all heretics by torture a confession of their own guilt and a betrayal of all their accomplices (1252).
As to the property of the condemned, if they are laymen, let it be confiscated; if clerics, let it be applied to the churches from which they received revenues. But those who are only suspected, due consideration being given to the nature of the suspicion and the character of the person, unless they prove their innocence by a proper defense, let them be anathematized and avoided by all 1-intil they have made suitable satisfaction; but if they have been under excommunication for one year, then let them be condemned as heretics.
• Rome, Italy, Feb 19, 2010 / 02:03 pm (CNA).- The president of the Pontifical Council for Promoting Christian Unity, Cardinal Walter Kasper, announced this week that Pope Benedict XVI will visit the Evangelical Lutheran Church located in Rome on March 14 for an ecumenical celebration.
• Pope John Paul II took part in a normal Advent service at the Evangelical Lutheran Christ Church on Dec. 11, in which he bowed toward his head and joined with Pastor Meyer in reciting the Apostles' Creed and the Lord's Prayer. In reference to Luther five centuries after his birth, the pope said, ''we see as if in a distance the dawning of the advent of a reconstruction of our unity and community.'' (NY Times, December 12, 1983; http://www.nytimes.com/1983/12/12/world/pope-citing-hope-for-unity-takes-part-in-lutheran-rite.html)
►Past:
• How does a Catholic sin against faith? A Catholic sins against Faith by Apostasy, heresy, indifferentism and by taking part in non-Catholic worship....when he intends to identify himself with a religion he knows is defective." (Baltimore Catechism Q. #205; http://www.clerus.org/bibliaclerusonline/en/bli.htm)
• ...”in the case of simple people and those who are weak in the faith, whose perversion is to be feared as a probable result, they should be forbidden to communicate with unbelievers, and especially to be on very familiar terms with them, or to communicate with them without necessity.” (St. Thomas Aquinas, Summa Theologica, Article 9. “Whether it is lawful to communicate with unbelievers?” http://www.newadvent.org/summa/3010.htm)
• “...this Apostolic See has never allowed its subjects to take part in the assemblies of non-Catholics.” (Pope Pius XI, Mortalium Animos, 10,11; http://w2.vatican.va/content/pius-xi/en/encyclicals/documents/hf_p-xi_enc_19280106_mortalium-animos.html)
• 1917 Code of Canon Law: "It is not permitted at all for the faithful to assist in any active manner at or to have any part in the worship of non-Catholics." (1917 Code of Canon Law states: that:Canon 1258)
• Canon 229 §1. Lay persons are bound by the obligation and possess the right to acquire a knowledge of Christian doctrine adapted to their capacity and condition so that they can live in accord with the doctrine, announce it, defend it when necessary, and be enabled to assume their role in exercising the apostolate.
• We furthermore forbid any lay person to engage in dispute, either private or public, concerning the Catholic Faith. Whosoever shall act contrary to this decree, let him be bound in the fetters of excommunication. — Pope Alexander IV (1254-1261) in “Sextus Decretalium”, Lib. V, c. ii: http://www.theologyweb.com/campus/archive/index.php/t-51631.html
See Roman Catholicism's attitude and regulation of Bible reading here.