Trolls eat votes. People see a horrendous post and think it's important to downvote it, not knowing that it's already got plenty of downvotes. This is significant to those who are on a vote budget.
Doesn't the same hold for good posts? People find it important to upvote good posts (even more so than to downvote bad notes - just look at the number of upvotes vs downvotes). High level monks eat votes as well - they eat more than trolls. If you consider "vote budget" to be a real issue, you should argue for a limit on
both sides: once a node gets more than X upvotes, or more than Y downvotes, voting on the node closes.
As an alternative, I would propose that posts by Anonymous Monk have a minimum reputation limit of -9. Once a post has reached that limit, the downvote option is disabled. That would act as an indicator and also eliminate the negative-rep badge incentive for Anonymous trolls.
The few trolls that would actually care about node reputation (doubtful - real trolls care about responses) and would be bothered by the reputation limit would take a few seconds to create an account. Just go to the sign-on page, enter an email address of 'troll@mailinator.org', collect your password, and you're off.
I also think you're solving the wrong problem. Trolls are not the problem. Troll droppings are: the replies. And considering there are always people eager to reply, the damage will be done before enough downvotes have been collected. For a flag to warn people about the existance of a troll, you need the flag in place before people can reply. So you might want to disable making replies before a node is at least X hours old, for some X. Which I don't think is what people really want.