Eventually they are going to find that there's a limit to how much violence you can incite before getting slapped down, legally or otherwise.
This doesn't mean 'planning a coup' is one of these contexts, but you are focusing on a very narrow example of the broad social system impact of anonymity in online communication.
Other than anonymity, talking to people who have no incentive to karma-farm is very refreshing.
In websites like Reddit/HackerNews, the karma system gamifies posting. You "lose" if you post any wrongthink, and you "win" when you reiterate whatever is socially acceptable.
This means there are consequences to posting. In *chan websites, there is no consequence to posting your thoughts (or just trolling, because that's fun sometimes).