concern troll

Noun

 * 1)  Someone who posts to an internet forum or newsgroup, claiming to share its goals while deliberately working against those goals, typically, by claiming "concern" about group plans to engage in productive activity, urging members instead to attempt some activity that would damage the group's credibility, or alternatively to give up on group projects entirely.

Verb

 * 1)  To troll as a concern troll would.