People like porn. There's a market for it. Even in a porn shop, if you put certain kinds of porn on the shelf, you are going to get funny looks. Also, people are hesitant to be that forthright about their weirder fetishes. The internet is anonymous. Meaning that there is a profit to be made from providing a desired product to the people who have weird fetishes. And as a general rule, it's harmless. Even if it offends our sensibilities, honestly, it harmless to children as well. So is there a line? Yes. Child Pornography, actual voyeurism, and real life abuse. But that's all stuff along the abusive scale. If its just along the weird scale...well just make sure everyone knows what there clicking on.