please don't call them "illegal" i know what you mean but it makes it sound like youre talking about actual illegal content and there are no laws about shipping, even if what you ship is "immoral" i dont see anything inappropriate (obvi so long as everything is sfw) about people having weird or unconventional toxic ships like bro/dave. theres a multitude of reasons why someone might be drawn to exploring that dynamic in fiction where it is safe to do so that arent malicious, many times it is a form of art therapy (that isnt to say there isnt a line to be crossed either). regardless you dont have to like it at all and you should just block users that post content you dont want to see, and to be honest a fair amount of incest ships are to be expected in this fandom due to the source material.