There are two site guidelines that apply to this. First, it's not ok to use HN primarily for political, ideological, or national battle. If a commenter is posting as you describe, we ask them to stop. Example:
https://news.ycombinator.com/item?id=20727426.
But by no means does it follow that a commenter behaving that way must be a sockpuppet, astroturfer, shill, spy, foreign agent, etc. That's where the second guideline comes in: the one that asks users not to insinuate these things in HN threads, but rather to email us at hn@ycombinator.com so we can look for actual evidence. Accusing others without evidence is a serious breach of the rules, and a personal attack. When people do that, we ask them to stop as well. Example, from the same thread: https://news.ycombinator.com/item?id=20727420.
Does that mean that abuse doesn't exist, or that we don't take it seriously? No—it does and we do. But the way we take it seriously is by looking for evidence. So far, such evidence as we've found on HN nearly always indicates that the commenter is legit—they just hold a view that some other commenters find so wrong that they can't believe it's sincere. (Corporate astroturfing is a different can of worms, btw, and I'm not talking about that here.)
Here's the most remarkable case we've seen of a mass influx of new accounts angrily defending "pro-China" views: https://news.ycombinator.com/item?id=20236444. Most users who are inclined to perceive astroturfing would have declared this an obvious case of manipulation. The only reason we didn't get an inundation of such accusations is that the wave of new accounts only showed up a day or two later, after most readers had stopped looking at the thread. But even this case, when we followed up on the evidence, turned out to be something quite different. I emailed every one of those commenters who had left an email address in their profile, and many responded. It turned out that the study under discussion had gone viral in China, someone had posted a link to the HN thread to the Chinese Quora-equivalent, and the new accounts were people who had found their way to HN from there and created accounts to speak their minds. I also posted in the thread asking the new accounts to explain how they'd come to HN, and several replied with the same story. Does that prove they weren't communist agents? No, nothing would prove that. But the null hypothesis—that people hold their views sincerely—was amply supported by the evidence. This was an extreme case, but over and over, the story we see is like that. Ornate machinations add zero explanatory power, but invoking them poisons the community; therefore we ask users not to invoke them.
Most people hold the views that they do because of their background. HN is a large, international community, orders of magnitude larger than your or my circle of acquaintances. What are the odds that in a group this large, quite a few people will have different backgrounds than you or I, and thus hold different views? The odds are basically 1. That means you're going to hear some "pro-China" views here, because there are users whose background connects them to China—by birthplace, family, education, work history, you name it—in ways that HN's Western audience mostly doesn't share.
Because this is happening, we have to decide what kind of community HN should be. Should we ban accounts, or allow them to be persecuted, for "pro-X" views where X is outside, say, a standard deviation of what most people here take for granted? Or do we want to be a pluralistic community that is strong enough to hold space for such views, and such people, even when most of us disagree? It's unclear which way HN is going to go about this—sctb and I can't control HN, only try to persuade—but I know that I'm only interested in participating in the latter. The other way leads to a community in which it's ok to smear others (such as a nation or ethnicity) and have mob attacks on innocent individuals: see https://news.ycombinator.com/item?id=19403358 for one example that turned out ok; unfortunately there have been others which didn't, and users have been run out of town. I don't believe anyone here wants those things, but the tragedy of the commons will take us there if we don't all consciously resist it.
https://news.ycombinator.com/newsguidelines.html