Failing to fight off the urge to say 'Journalist' I'll move swiftly on to a personal favorite: Jeremiah. It's a term that is falling out of use and I think that's a shame because it fits the needs of this question so well. Here's the entry from the OED (with a few of the examples):
...used allusively to denote a person given to lamentation or woeful complaining.
1905 Daily Chron. 1 Sept. 5/7 The Jeremiahs have been on the rampage; the dismal and the doleful would-be experts [etc.].
1928 Daily Express 23 Feb. 3/5 There are always Jeremiahs who go about saying that we have never had such bad times.
1963 Times 22 Apr. 8/5 Mr. Selwyn Lloyd..wanted to see Young Conservatives ‘rise up in protest against the Jeremiahs, defeatists, pessimists, denigrators’, [etc.].
Another unusual word that may be consideration is vituperator, from the verb vituperate - OED again:
To blame, speak ill of, find fault with, in strong or violent language; to assail with abuse; to rate or revile.