Inviolate evil: request for word from definition.

Hi, I'm trying to find a word that fits this defintion:

adj.-So definitively evil as to prohibit discussion (of its particulars).

So, consider sacrosanct-the word of God is sacred and so items like the world's creation are not up for discussion. Now consider items where the same applies but because the item in question is the antithesis of sacred-i.e. one may not discuss Hitler or Satan's human qualities as it violates the notion that they are embodiements of evil.