There can be a big difference between those things being legal, and the society lacking the law or justice system to enforce those things as illegal. I think the latter would be an easier pill for an audience to swallow because you can have many characters who don’t have to feel complacent with these acts being the norms. Dystopian societies already involves inherent suffering and or oppression. Also, there are ways to write of this that isn’t the first image as “guy on bath salts rapes 9 year old daughter nightly” and “subsection of society practices arranged marriage cross generationally between cousins” - the second being quite similar to many practices already having occurred in human history. The people in power angle you added in the sub posts don’t require law to be involved. People in power will do what they want regardless of what’s legal.