it alleged that local developers cannot compete on Steam with international developers, because those do not have to apply the local regulations:
That’s not really contrary to the point, but orthogonal to it. Steam is outcompeting on the basis that it receives special privileges on the basis of its international status. It’s still outcompeting because of a resource advantage. But that advantage exists because domestic developers are disadvantaged by virtue of national regulations over domestic developers.
what is my opposition that doesn’t encompass a de facto defence of free market capitalism? The damage to the users. What about all the Vietnamese people losing access to Steam’s online features, which are arguably necessary nowadays for many games, especially multiplayer ones.
Your argument is the same kind of “consumer rights” argument that I’ve seen everywhere on the internet, because you are implying that there is material harm to the people of Vietnam caused by Steam’s banning. Which is a fairly specious argument. It’s the loss of a luxury item. No one is materially harmed by it. It’s not like Vietnam banned insulin. And while you may not use the same language, you are effectively saying that every consumer on the planet should have free access to the best products available for whatever “thing” they want. In this case, video games. It’s a de facto argument for free market economic policies.