JP did say that he's got "a TON" of things to check that the thread doesn't do suicide for nothing but I've also seen rather good threads go suicide because of one stupid post... I wonder if JP's algos count the number of negged posts in a thread, that would solve something.
Also if AP's could given to an entire thread, not single posts, users could balance threads they think are too negative. Those AP's would then actually fall into a black hole affecting NOTHING but the thread.