Question

How might the US government use a law like the Sedition Act today to suppress speech it disagrees with?

Answer 1

If  the US prioritized the profession of loyalty to the current government more highly than it prizes First Amendment rights of free speech, something like the Sedition Act might be presented to the American people as an act of patriotism.

The Sedition Act of 1918 was passed to squelch voices in the US that was perceived as interfering in any way with the nation's war effort as a participant in World War I.  Legal scholars now see that act as contradicting the First Amendment.  Indeed, the Sedition Act was repealed in 1921, only a few years after its passage.

But there have been hints in recent years, in regard to what is called "the war on terror," that Americans will tolerate restriction of some civil liberties if they think their security is at stake.  The USA PATRIOT Act, passed in 2001 (after the 9-11 attacks), included measures that allowed the government much leeway in regard to surveillance of electronic communications.  The American Civil Liberties Union continues to challenge these sorts of aspects of the PATRIOT Act.