And who is going to keep the comments on track? The typical anti-US people will come out in droves to derail. So we'll end up with the same issues, but instead we'll have political filtering done on the accepted articles themselves that could generate bias.
Its not like all these people will suddenly stick to the topic. In fact, I find many articles that involve India, China, Russia, Brazil, etc usually have a top comment of "But the US is worse." There's a lot of knee-jerk anti-US sentiment here and filtering things out isn't going to change that.