>>> ... but who are the professional counter-trolls?

The actual journalists, at least the ones that wade into the swamp of comments sections. The vast majority of real journalists shirk any duty to respond. That's a big mistake imho.

Also google and other search engines, at least insofar as they are looking to revamp search results to promote actual stories and drive down junk news. But there is another link on HN today about the dangers of allowing search engines to become the arbiters of truth.