I think I get it now. In order to not admit that they are horrible people doing very illegal things they have to think of the victim("Roku") as a subhuman pervert.
But if it was ever revealed what they were doing in context then they'd be the disgusting ones.
I don't think it would even matter to this kid that he's about to sadistically torture his biological father sexually, just as long as nobody else finds out about it.
So yeah, this house needs to burn to the ground with everyone but Daisuke locked inside.

Base +8, Gemini81 +7