Is this purely bluster? Perhaps.
But so far the President-Elect has tried to do the things he promised to do during the campaign, even the bluster. For example, he followed through on the racism bluster by nominating a white nationalist (Steve Bannon) as Chief Strategist. He has followed through on the Islamophobia bluster by nominating someone who believes Islam to be a "cancer" (Michael Flynn) as National Security Adviser.
Therefore, it's not entirely outside the realm of possibility that he will try to take steps to weaken other First Amendment freedoms once in office. These might possibly eventually include freedom of assembly and freedom of religion.
It is not a partisan opinion to state that threatening jail time or the revocation of citizenship for those who exercise their First Amendment civil liberties is clearly outside the traditional norms and boundaries of liberal democracy (as offensive as flag burning or other forms of expression might be to us). Right now the President-Elect is calling for jailing or revoking citizenship of those who burn flags. What happens when he calls for the jailing of religious leaders who publicly oppose his rhetoric or national security policies? (Examples: here, here, and here.)
As someone who believes that liberal democracy is a preferably form of government to autocracy or authoritarianism, I see rhetoric like this to be clearly harmful to liberal democracy whether it comes from Republicans or Democrats or anyone else. Even though it may just be bluster, the evidence so far is that our President-Elect believes the things he blusters about and will try to implement them.
Therefore, it is worth taking the President-Elect at his word and worrying when he threatens to weaken or undermine the core tenets of liberal democracy, including First Amendment freedoms.
An earlier version of this post was published on the author's personal blog here.