I'm not sure how much reliability a "de facto" leader has, as much power I suppose as the ALA actually has over individual libraries--which is as much as the library's staff chooses to let it have.
I am a librarian and I'm also a member of the ALA. Even the most strident of ALA devotees do not follow every single thing the ALA endorses (though I do agree wholeheartedly that most librarians are decidedly liberal and the ALA promotes liberal agendas).