I realize the answer could very well be "since forever", but I'd like to know when slapping, spanking, choking, or otherwise abusing or degrading women during sex became socially accepted? My guess is this really began 20 years ago or so with free access to unlimited online porn.

I ask because my first experience with sex was abuse, and I grew up thinking that's what sex was - that it was degrading and dehumanizing by default. Now after doing a lot of research I'm thinking it's not actually supposed to be like that and I'm wondering when violence and sex became so conflated and socially reinforced that they've become the same thing.