It's a futile effort when you have 100,000+ posters. Try herding cats for an easier task.
I disagree. I've seen it work on threads before. It doesn't work overnight, but if enough posters do it, it helps keep the lid on flame wars - and if some folks persist in flaming, they tend to be the ones who are deliberately engaging in a flame war and not folks who are getting over-emotional on a given thread.