Justice Gorsuch in his concurrence specifically commended the court for doing so, believing that a content manipulation argument could run afoul of first amendment rights.
He said that "One man's covert content manipulation is another's editorial discretion".
EFF's stance is that SCOTUS's decision based on national security ignores the First Amendment scrutiny that is required.
> The United States’ foreign foes easily can steal, scrape, or buy Americans’ data by countless other means. The ban or forced sale of one social media app will do virtually nothing to protect Americans' data privacy – only comprehensive consumer privacy legislation can achieve that goal. Shutting down communications platforms or forcing their reorganization based on concerns of foreign propaganda and anti-national manipulation is an eminently anti-democratic tactic, one that the US has previously condemned globally.
I think it's more about the fact that users of platform are able to connect and share their experiences and potential action for resolving class inequality. There's an entire narrative that is outside of US govt/corp/media control, and that's a problem (to them).