What you are saying makes sense, but I am only commenting on this in relation to freedom of speech. The government is the government whether it is local or state. So in terms of freedom of speech this is the same thing. In terms of the constitution, local governments are completely subject to the authority of the state government. There is no sharing of power like at the federal/state level.

I think it all has to do with impact. The point of the first amendment is so that the government cannot create policy to chill speech it doesn't like. That's why we all appreciate it.

A small branch library making autonomous choices about what books to store behind its walls with backing of the local community doesn't stand to chill speech across the state or nation, so the first amendment protection to free speech isn't really implicated. If some podunk town doesn't want to put books about trans kids on the shelves, that's not going to chill speech about trans people across the state or nation.

But when the governor sets policy that no libraries shall have books about trans people, then that's going to chill speech and the first amendment is implicated. Therefore it's unconstitutional, despite flowing from the same derived power source. That's my view anyway, I'm not a lawyer.

A law must abide by the constitution.

Community norms are not laws, and are much more flexible, have no government enforcement mechanisms, and don't have the weight of the legal system behind them.

These are very different things when it comes to freedom of speech!