Regardless of Nazi anything: community guidelines state no posts from X.

They have a right to ban posts from whatever website they wish for whatever reason they wish to do so - it’s their community. They weren’t saying the person couldn’t have hosted the same comic on Imgur and posted it. He got banned for arguing back, not for the contents of his comic. It’s rational that any community would ban any idiot who is breaking their guidelines and being rude about it.