Ahhhh. A Graphical Night (Elie Weisel) then. That's considered obscene? It was required reading for me growing up. Understanding the plumbable depths of human cruelty was considered a worthy expenditure of the education system's time... Might be different now though.
Maus was subject to one of the many ongoing book bannings in the United States and was removed from multiple libraries due to containing "adult content."
It's got some depictions of violence that I think parent groups object to, so that kind of obscenity. There's technically nudity in some of the dead bodies I guess?