I disagree. Things are ONLY wrong if they cause definitive harm. I don't think incest comics fall in this category.
Just because you find something wrong doesn't give you the right to apply this morality, then, to everyone. And while I certainly agree that most people would shun this kind of thing, I also believe that there are completely harmless people out there doing no wrong to anyone who enjoy this kind of stuff. They lead their lives, they don't hurt people, they don't commit crimes, etc. And yet they have an uncontrolled attraction to things like incest, or others. As long as this remains in the realm of fantasy, good for them, IMO.
I'd also not consider incest wrong in itself unless rape was involved, someone was underage, or there were fertility issues. I don't think it's right to birth children from this kind of union, that would be harm caused. But two people, brother and sister, who are consenting adults with no chance of conception, who just want to have sex... Personally, I think that's their business, though I think they might look into a psychiatrist. I wouldn't jail them for doing something that I find arbitrarily wrong. If it doesn't cause harm, I can't justify illegalizing it.