Is to benediction as harangue is to praise.
blessing
clamor
philippic

Philippic.

Explanation:

Harangue is a long, lengthy and also aggressive speech given by someone, which is quite contradictory to that of praising someone.

Likewise, Philippic is when someone launches a bitter attack, that to, verbal, on someone. This is opposite of the very nature of giving a benediction. A benediction is when the minister of a church gives a prayer of blessing on the congregation at the end of a church service.

So, the answer will be philippic is to benediction as harangue is to praise.