That said, I don't think it's even remotely reasonable to call someone "sick" for looking at pictures which are attractive to them.
Now then. We do have laws about exploiting children (i.e. child pornography), which I completely support. However the purpose of those laws is to prevent children from abuse, especially from that at the hands of older people in positions of power. And it's not limited to sexual matters either. We likewise do not allow minors to purchase airplane tickets, to rent motor vehicles, to enter into legal contracts, to get tattoos or body piercings, or to purchase hazardous goods like firearms, fireworks, dangerous chemicals/medications, alcohol, and tobacco. The purpose of the law is to protect the 'innocent'. Given that artwork does not involve any harm to any person (of any age), I fail to see how those laws would even apply.
Now, is there some smaller % of the art out there which ventures into "sick" territory". In my opinion, yes. Absoloutely. But there has never been a study that has found that people consuming that sort of fictional media have ever gone on to do anything in real life. If anything I'd think the opposite would be true. Fiction allows people to explore things that they cannot or would not do in real life. It provides a 'safe' outlet because no actual people are being harmed. If you know of a study which suggests otherwise then please link it, I'd love to read it.