A troll (no matter how low-level) wastes time, ruins people's mood, and destroys trust.

Every actual troll increases the probability that some other innocent newcomer will get accused of trolling wrongly, making a community just that tiny bit more hostile to newcomers, and thus less open to the outside world. Then those newcomers judge the community badly for the community's negative judgment of them. Bad feelings all around, and a community which is now less receptive of new ideas, because they might just be trolling.

So, yeah, trolling does damage. Trolling is bad, bad, bad.