I'm just gonna say the primary reason there is a sex taboo today is because a monk in the middle ages convinced the man who would become pope that sex is a sin because it propagates the human race and by extension original sin. Before that sex was an open and freely discussed topic. Also for the better part of human history families lived in single room homes. Also based on current evidence early human society was closer to bonobo society (ie. sex used as a form of bonding and conflict resolution.) Then you get things like "abstinence first" sex-ed that literally made one of my friends swear off sex and romantic relationships completely. Then you have people like one of my acquaintances that feels they have to "punish themselves for having any form of sexual urges. I think at this point we should be trying to end the taboo.