Why does the Chinese Communist Party Suppress Speech with which It Agrees?

The Chinese Government celebrated International Women's Day today by detaining several Chinese feminists to prevent them from holding rallies to draw attention to the sexual harassment of women on public transportation. I am new here to China, having been teaching constitutional law in Shanghai for barely over a month now: It is not a big surprise, therefore, that I am baffled by the Communist Party's suppression of public speech with which the Party basically agrees and that is not directed against the Party itself.

The Party leadership, after all, holds no brief for sexual harassment. They have made suppression of domestic violence one of their regulatory goals. The campus where I now teach in Shanghai has brought in feminists like Catherine MacKinnon this term to speak to lecture halls crowded with their students about the evils of prostitution in China and elsewhere, without any murmur of discontent from any party official. Moreover, Li Maizi, one of the detained feminists, is not, to my knowledge, especially anti-Party: Her public demonstrations mostly focus on the bad behavior of private males, not governmental officials -- the same bad behavior, in fact, that those officials have tried to suppress. Why, then, detain Li rather than enlist her?

There are no shortage of hypotheses explaining this odd Party tendency to bite the hand that agrees with it. The problem is that every hypothesis seems no more plausible than its opposite, and data are scarce to falsify or confirm either. Perhaps Party leaders just do not like any unlicensed private speech from any NGO, regardless of its message, because such examples could encourage wider disorder. (But why not believe that speech can reduce social tensions just as well as inflame them?) Perhaps Party leaders look on any public protest about conditions in China as a threat to the CCP's collective "face" or reputation. (But what could be a worse blow to mianzi than the detention itself and the blowback that the detention invites?) Perhaps Xi Jinping's effort to tie the CCP to traditional Chinese values has made traditional patriarchy an unspoken norm of the Party.

As I say, I really have no idea, but I am interested in anyone else's thoughts -- especially if they have something better than the just-so stories that I (or anyone else) can easily invent but not really confirm.