It became mainstream in that religious inhibitions between couples have vanished, except for some stupidly conservative sects. Only fanatics still believe that masturbation is sinful, or that women shouldn't reach orgasm during sex. Or talk about these things, for that matter. Another aspect of the sexual revolution, namely birth control, is alive and well but still resisted by idiotic conservatives - and yes, I'm insulting Catholics here as well as fundies. Abortion is another part of the revolution, and that is still a battleground.
When porn became legal, that was yet another manifestation of freer attitudes and legislation. Porn has been around since antiquity, and photographic porn appeared almost as soon as cameras were invented. But it was criminal to own it until about 1970.