If they are just people with an opinion, they can state that opinion, no problem. If they want to harass, threaten, and beat up those with a different opinion, well, you can't do that here. The next question is why they do such things. Because they're so enraged because someone criticizes China? Because they don't know the rules here, and don't bother to learn? Or because they actually are agents? The last seems the most likely. (You don't see, say, French students in the US brawling with French expats who criticizes France.)