Perhaps you don't feel like this matters, but I can tell you for a fact that people have been hounded off this site by comments of this nature (e.g. China-related slurs), including extremely ugly personal attacks. I don't want to have anything to do with a site where that happens, and I don't believe that the vast majority of this community would either. None of us wants that community. But we can easily end up with it anyway, if we're not careful, because that's how group dynamics work.
Part of the problem here is that the forum feels like an intimate conversation, and in intimate conversation there is more latitude for talking in a grand and speculative way about this stuff, especially if you have high trust from previous interactions. But when you post to HN what you're actually doing is broadcasting to millions of people. Public broadcasting has to have different standards. Imagine what would result if a million people heard the things that you (or I, or any of us) said to your friends, without any mitigating context.
I don't know what you mean by political expediency but it doesn't sound like something the moderation job is replete with.
In reality, for this specific topic, the canyon is not so wide as you believe and I don't think you have the relevant cultural context to make such a judgement call on how wide it is. It's a century old question... how much freedom of speech and how much censorship and at what cost?
In this case you chose to censor something that could potentially be flame bait (but wasn't) at the cost of preventing any discussion about a very real and general truth about China.