The limits of discussion

I spent a little time today reading some popular blogs by young up-and-coming anabaptist theologians, and the radical nature of some of the things they said made my mind wander to a conversation I’ve had several times with a good friend of mine. Before getting to the thought itself, I want to quote something from Peter Leithart’s The Promise of His Appearing: An Exposition of Second Peter:

One of the main threats facing Peter’s readers is the emergence of false teachers, and refuting the false teachers becomes the focus of his attention throughout chapter 2 and into chapter 3. “Refuting,” though, is not quite the word for Peter’s language; pummeling, denouncing, castigating, condemning, attacking, and assaulting are more accurate description of what Peter does to his opponents. He offers a few arguments in response to false teaching in chapter 3, but chapter 2 is mainly occupied not with refutation but denunciation of the most severe sort. This chapter contains some of the harshest rhetoric in the New Testament. Peter does not think the false teachers have an argument that needs to be considered carefully and responded to point-by-point; he does not try to be balanced or “fair.” Though the chapter is alarming to modern sensibilities, Peter’s vehemence is just the outgrowth of his deep pastoral commitment–when he looks at the false teachers, he sees nothing but a blur of white fangs, claws, and gray fur beneath the covering of wool, and he girds himself to make war on the wolves.

The issue is probably obvious: how do we know what point we ought to switch from “discussion” to simple denunciation? When do we stop treating people as wandering sheep and start treating them like wolves in sheep’s clothing?