That's the proximate cause (or one of them, in my opinion), but I think what's interesting is how that came to be. I mean, disliking Bush is pretty mainstream around the world, but the sort of frothing at the mouth attitude at reddit isn't. How did the extreme come to dominate?
This is one of the rare cases where reddit does worse than digg. Digg's frontpage ranking algorithm (newest-first rather than bubble-up) means they have to have a way to bury stories. Reddit doesn't. But that means it's vulnerable to a group of a few hundred ultra-dedicated zealots.
I have some ideas about how to fix this (without digg censorship). The news sites we have now are still only version 1s.
I wonder if it was just the first group to dominate at reddit meant that it they would always downvote submissions that didn't confirm their outlook, attracting more people with a like mind, and repelling people with differing opinions.
If I owned reddit I would have modified it so that you could have blocked submissions from people or sites you didn't like. That would have helped make it bearable for people like me.
A "tipping point" in other words. That seems plausible. I think the problem with simply blocking people and sites is that the site still "tips", and you end up ignoring too many people. The happiest people are those who dont' have to ignore anyone.
Which brings up another point - do you really want to foster debate? Maybe it's better to just feed people what they want. If I can't have thoughtful, considerate, and informed debate, I think I'd rather just have the echo chamber than impolite, rude, paranoid extremist rants.
I have a suspicion that most if not all of these communities go downhill when the number of people involved starts to really go north of the "monkey number":
As someone comments, stumbleupon is a little bit better, because instead of having one home page for N people, which simply cannot scale, you are more closely connected to people who share your interests. I'm not sure how that works out for news sites, though.
Part of the problem may be that, initially, concentrating your user community might be the only way to go beyond a critical mass of users, but then as growth continues, you do want to spread people out.
PG, please keep YCNews focused and keep it niche. More people and wider subjects will just diffuse the relevancy of content.