I'm almost always on the pro-Janitor side of these debates.
But today, I am with the OP. The instant you say "posting tohou should be a bannable offense because I don't like tohou", you pave the way for the banning of personal preferences rather than actual rules violations. And Tohoufag violated no rules. So where do we draw the line? Non-Tohou anime images become banned, then non-anime Japanese artwork becomes banned, then Japanese-themed characters like samurai and monks become banned, then a Western-themed character gets banned because it was loosely inspired by a Japanese character, etc.
Moderation should be there to keep out porn and /b/-shit, not the mod's personal pet peeves.