Earlier quoted context omitted.
Avoiding patrons from being tracked/potentially in the future prosecuted for their reading is professional ethics for librarians, pretty much regardless of political alignment.
That's interesting and new to me, as I'm not American. Does the American government track or prosecute people for their reading habits in libraries? Is it to be expected then that librarians are aligned to the political left?
The biggest professional organization for them in the USA (the ALA) is not officially politically aligned, but some of their core positions, notably privacy, intellectual freedom and anti-censorship have of late have come to be seen as politically left and in the States especially more aligned with the Democratic party.
Demographically librarians in the United States do lean liberal but I don't know that they do at any higher rates than other educated people.
Finally, this is not just an American thing. The IFLA has very similar positions on privacy, intellectual freedom and censorship and monitors those positions around their world.