THIS is what this is all about gentlemen.
This sort of arrogance, selfimportant "messiah" like attitude. I myself am guilty of radiating it, but I've heard and seen enough of this sort of attitude to make me sick of recognizing it. It's the sort of mentality that allows you to think that your manga, anime or fandom of choice is somehow better or worse than the next guys. It's bound to cause collisions.
This sort of public display also forces bystanders into a position where they gradually will have to lean over to one side and chose whom to support. It's a never ending circle of trolling and hate that just leads to more meaningless BS in a chase for a free spot to actually discuss your beloved subject.
IF Touhou really has a manga and the manga isn't any anomality according to the rules it should of course be allowed to post here, just as Bleach, or any other ANIME or MANGA out there.
Now I also believe that moot created /jp/ for a reason, and out of whatever material this net of reason would constructed it seems that it has caught some things related to Touhou. If those things were just posted in their designated board according to the rules, and the /a/ related stuff were posted in /a/ I firmly believe everything would be alright.