I'd be surprised if that helped very much in cases like the one under discussion, given that nothing stops people from creating new accounts. That's enough to stop casual spammers, which is great, but I'd expect anyone willing to sink hours into writing comments to also be willing to create new accounts on demand when their karma got too low.

More generally, I'd be surprised if any change to the karma system itself rendered us significantly less vulnerable to that sort of dedicated resource-grab without introducing negative side effects.

My own feeling is that the best immune system is cultural, here. To the extent that LW members find participating in discussions like that one valuable (there's a defense of that position here, for example), we will continue to periodically experience such discussions.