It seems kind of odd to argue that there are moral ways to have slavery, especially in a porn game, since the entire concept of slavery is inherently immoral and there isn't much point to a porn game without sex.
It's quite simple really, sex is between you and her, photos are going to get sold off for anyone to see.
Your girl/boy might fuck you, doesn't mean they want photos of them for all to see.
I mean really dude, there is what a dozen chicks, all of them perfectly fine with you fucking every other girl in the game, where is the logic in that.
I mean fuck by the end of the game you will have fucked one of those damn crazy jebus lovers that say dumb shit like you shouldn't masturbate.