The problem is that internet readers are far, far too prone to classify others as being in bad faith, so in practice, "drawing the line" usually amounts to a provocation. This bias is so strong that I don't think people can be persuaded to draw that line more accurately.

Moreover, the concept of good faith / bad faith refers to intent, and we can't know for sure what someone's intent was. So the whole idea of assessing someone else's good-faith level is doomed from the start.

Fortunately, there is a strategy that does work pretty well: assume good faith, and reply to bad information with correct information and bad arguments with better arguments. If the conversation stops being productive, then stop replying. Let the other person have the last word, if need be—it's no big deal, and in cases where they're particularly wrong, that last word is usually self-refuting.