There are tradeoffs to protectionism that are inherent disadvantages in the strategy itself that doesn’t need someone to make it a disadvantage. Otherwise all countries would be protectionist all the time.

Tik tok dominating is just good old outcompeting the competition.

Protectionist strategies create less domestic competition, resulting in underdeveloped industries that would die off in the face of real competition. So if Chinese companies are insulated from outside competition then in theory they should have a harder time developing globally competitive products. If we continue to allow TikTok and other Chinese products it is not without inherent benefits of increased competition driving better domestic competitiveness.

Of course it just all looks like we are getting screwed because TikTok is outcompeting despite all this, but banning or hobbling it will just make Facebook et al complacent and likely even less competitive in the global market.

We need the competition, basically, if for no other reason than the fact that a competitive market is what underpins healthy capitalism.

Plus, subsidies are simply another form of protectionism and the US heavily engages in this too. We can’t pick and choose when protectionist policies are applied because everyone is doing it in certain industries.