It's easy when a community is small. The more prominent the community gets, the more it tempts people who enjoy stirring things up.
In the end I'm not sure if any moderation scheme can prevent that, to be honest. There will always be people who consider it a challenge to see what they can get away with, either by trying to stay just under the moderators' radar or by returning every time they're banned. Provocation makes people defensive, and then their own replies turn harsh, contributing to a negative perception of the community.
I do hope that this community avoids it as long as possible. I've discovered it only recently and am enjoying it. But past experience suggests that it, too, will one day degrade.