I think you might want to move away from sexuality for a moment and consider taking a member of our society's life in order to understand @RichardGibbons' point. Citizens of Greek and Rome who were fathers had total control over their household. If they decided their child no longer deserved to live, they were allowed to do what they saw as necessary, same went for servants. This is because they weren't viewed as a part of society.
To hit this point home for myself I ask, "what group might we not include as a part of our society today that future generations will judge us for?" The simplest answer to me is a pig. I am a carnivore. I eat meat, I invest in companies that might abuse animals and that for sure kills them for a profit. Do I personally have a problem with that? The abuse, yes. The killing, no. This is because I don't view animals as part of our society. Kill a pig, it is fine. I like bacon. However, my daughter (age 3) might have a huge problem with this one day. Will she be right or wrong? I believe, if everyone agrees with her and mandates that pigs can no longer be killed for food but only had as pets (or whatever), she would be correct. My belief about a pig's inclusion into society doesn't matter. Society has determined that a pig is part of it therefore I shouldn't kill it or eat it.
Now what is ironic about the pig argument is that this was a moral law from God. Then Christians claimed it to be okay, mostly because they realized how good bacon was, but a little bit because they misinterpreted God when he told Peter to eat the unclean meat. Then Paul got all "moral relativist" by saying that Jews need to keep the law and gentiles don't need to. But that could be a topic for later.
Do I personally believe I have the capacity to view a pig as part of our society and thus taking its life is morally wrong? No. However, do I view my daughter as part of my society and would prefer to do things to not upset her if I view them as benign? Without a doubt. To me, that's how society evolves. Enough children convince enough parents that an aspect of society is worth compromising on and society becomes change. Eventually all the bacon lov'en holdouts will die and now the pig is a part of society, killing them is and was always wrong and the whole of humanity will judge us and our forefathers; this will become a proof that Muslims and Jews were correct and everyone else was wrong.