Fr. Ambrose was not banned for defending himself. He was banned because while under post moderation, he began harassing various moderators publicly and privately here and elsewhere, and posting inflammatory profile signature lines repeatedly.
If he were not a respected hieromonk, he would have been banned years ago. This was simply the "last straw" and the culmination of multiple "ticketed" incidents. It has nothing to do with siding with heretics over Orthodox, alleged moderatial malice, or not wanting to give a man a chance to defend himself. It was the totality of his posting which led to this decision, not one isolated, one-off act.