However, there are some people who look for plagiarism by people that disagree with them, and/or that are critical of them.
Of course there is, I admit it. But these are ideological people, it does not matter for them who to look for plagiarism, they are against any plagiarism. And this troll is looking for plagiarism only from the participants of some kind of signature campaigns. That makes all the difference.
I am not sure I agree with your conclusions.
Those that look for plagiarism by people who disagree with the person are not against "any" plagiarism, they are aginst people who think differently, and who criticize them.
I would also point out that in the past, DarkStar_ has offered bounties for people who are able to find substantial rule-breaking that results in a participant being removed from his campaign. So there is a financial incentive for people to look for things such as plagiarism, alt accounts, and other frowned upon behavior by those in the CM campaign.