In the case of marriage the start of the slippery slope was the 1930 Lambeth conference in which for the first time in history contraception was accepted as moral by a major religion. (The fact that people did it long before is irrelevant. Sin has always been with us, but this was the first time this particular sin was declared to no longer be a sin.) It accelerated in the 1950s and 1960s with no-fault divorce, and the final "tipping point" came in 1968 with the definitive rejection by both clergy and laity of Humanae Vitae, with the clerical rejection being the fatal turn.
Events since them have simply been the inevitable consequence of that tipping point, as clearly enumerated in that remarkably prescient document itself.
God never once in any book of the old or new testament condemned contraception within marriage, the only mention of it in either book is the story of Onan who was punished for his selfishness, not simply because he used birth control. He was Ordered by God to produce heirs with his brothers wife, and refused, and was punished by God for defying his explicitly ordered will, not because he used birth control.
NO doubt sin has always been with it, but to argue birth control destroyed marriage is disingenuous.
Birth Control and Marriage existed long long long before the modern teaching that you shouldn’t use it if married. If marriage is an institution of God and birth control itself within marriage is an affront to God I am pretty sure the Bible would have mentioned it explicitly. The Bible states explicitly that laying with your wife while she is menstruating is a sin, but I don’t hear the church(s) condemning any one for that. It explicitly tells you not to cut your sideburns or beard, but most Christians I know do not have beards or sideburns... these are things that the old testament EXPLICITLY condemns. Birth Control within marriage is never mentioned with the sole exception of Oman using it to willfully defy the explicit order of God to him for his own selfish reasons to not need to split the inheritance.
To argue that birth control within marriage is a mortal sin, would be to debase ever marriage that existed prior to this far more modern teaching that you may only plan your family by abstinence or timing when you decide to be amorous to your partners cycle and hope for the best.
Agreed. Plus the legalization of abortions only added to the viewpoint of severing the connection between the sexual act and the creation of life. I wouldn’t be surprised to hear pro-aborts start arguing along the lines of “abortion is necessary so heterosexuals can have the same rights as homosexuals in not worrying that their sex lives will ever result in pregnancy!”