from an objective standpoint China is a much nastier place than the USA for freedoms and human rightsI think it's important to question that statement. Consider that we learned in the past few years that the US has been routinely practicing "rendition" for decades... in other words, putting someone on a plane and flying them to a jurisdiction without any human rights protections, and doing all sorts of highly illegal, human rights violating things to them.
Also, the US has an interest in convincing the world (especially its own citizens) that it occupies the moral high ground. This is part of the American story. Americans will not tolerate wars that are about territory or resources, but we seem to have an infinite tolerance for wars that are about "good vs evil". Thus the moral high ground is the first step in any warmaking propaganda.
In an absolute sense, with routine rapes in prisons, rendition, the atrocities at Abu Ghraib and gitmo, etc., I seriously challenge your assertion that China is "much nastier".
Ironically, the reason China practices censorship is to limit the chances of widespread social uprising. People in the US tend to idealize the idea of revolution so much that our through process is "well of course they should have a revolution, then they'd all have freedom just like us". In reality, widespread social uprising in China would likely mean millions of people dead or starving and no chance of a gradual transition.
The reason China cracks down as hard as it does is b/c there are fault lines in its society that might crack and result in social uprisings and lots of people dying.
It is in the US's interest to try to poke at these and provoke them, to prevent China from proceeding gently into the modern age. This is why Obama feels comfortable starting a trade war that will lead to many in China starving, and why Paul Krugman forgets all about economics and calls for massive tariffs. Neither of these men care if people in China die as a result of their actions, and both will be the first to criticize China for its occasional crackdowns rather than praise it for its massive undertaking of nonviolent societal transformation into the modern age.
China's big problem is that as it liberalizes its economy there are some areas that have become very rich while others have remained very poor. If a social uprising along class lines were to emerge, it would destroy China. Unlike the US, China does not have geography conducive to domestic transit, thus its coastal areas are inevitably going to be far wealthier than its inland ones.
Is it unreasonable for China to try to stop social uprising movements? No more unreasonable than for the US to try to stop them. But to consider what is an equivalent movement, one must appreciate what a delicate balance China has undertaken.
In light of this, the sheer irresponsibility of Obama and Krugman comes to light. Google too is guilty of this, though I don't hold a company to the same standard.