1) In the case of obvious trolling or idiocy, e.g. "lol your mom sucks" or "ur dumb", downvoting below zero is warranted because those comments are stuff that we don't want to see at all.

2) In the case of everything else, downvoting is warranted, imho, only when something has been upvoted beyond where it should be. For example, if Jason's posts were at 50 upvotes, I would downvote them, because that's totally unwarranted. In this case, I'd downvote them even at 10 points... they're relevant because of who he is and how he's connected to this, but not that insightful.

Basically, for all non-troll posts, you should upvote/downvote based on whether you feel the post has the points it deserves, and generally never downvote below zero.

In this case, Jason, although controversial, is not an obvious stupid troll - he's responding to points that people are making. I would like to see his posts somewhere between 1 and 5 points, rather than at -4.