I have felt that this goes back to 1929-1930 Lambeth conference when the Church of England decided to accept artificial contraception. The minute you see life as an inconvenience you open the door for a myriad of sins.
American churches fell all over each lining up with the same CoE they disagreed with on everything else.
There were Fundamentalists who held out up into the fifties, but even they caved in the late fifties by just broadening the things they called "justifiable reasons" to use contraception.
I guess even Fundamentalists could see that people who stayed home to watch Disney on Sunday night rather than going to Sunday night service would leave the fold sooner or later if they resisted American culture and the push for abortion disguised as contraception. Now the consensus seems to be that as long as you use chemicals instead of a "tacky" one that requires assistance even the "morning after pill" everyone knows is an abortion in a capsule is Ok.