concern troll

Short definition from Wiktionary

Noun

1. 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 abandon group projects entirely.
2. 2
   Alternative form of concern troll.

Verb

1. 1
   To troll as a concern troll would.
2. 2
   Alternative form of concern troll.