I think loss of control is the 'quiet part' that you've hit on in this issue. Political regimes from Latin America, the Philippines, Myanmar, have used US based social media products to organize and incite harassment and violence against critics and minority groups. This is a lucrative and powerful racket that the current US administration is leveraging in a similar way and at Chinese expense. But if US eyeballs move to a platform owned by China you can envision them turning off the attention tap to vested and opposing US interests.