A "public library" is maintained by various means.

Some of them are supported by taxes.

More of them are supported by private fund drives, supplemented by local and state grants and aid.

"Public" refers to who gets to use the facility.

The Fourth will permit warrantless searches of government employees' workstations by the supervising government. It will not permit warrantless searches of the persons, belongings or records of private citizens who are the clients of the government agencies.

So, to recap:

If a public library retains considerable private funding, your point is inapplicable.

If a public library is entirely funded by the state, it is still inapplicable for the FBI unless we are talking about the Library of Congress, the only Federally funded library I know of. And even then, the only ones subject to the warrantless search are the employees and equipment of the LOC. The vast majority of tax-supported libraries are supported by local and state funding.

I, for example, am employed by a board of citizens representing my local community. I answer to a director who is not paid by the state, either. The state, however, oversees the running of the public libraries, including adherence to the state privacy laws, which this Federal end-run clearly violates.

And I assure you, any modification of procedures among librarians to eliminate records is far from arbitrary, but a defensive response to a Federal action that violates the rules under which libraries operate. Searches with warrants never presented this kind of conflict. A little tension, maybe, but there was common ground.

The records held by libraries and other public service organizations are not "secret" but "confidential". There's a big difference. "Confidential" means "protected; not public". It allows people to conduct their business in private. The files the FBI is seeking to compile through the seizure of confidential records would be an excellent definition of "secret", because no one is allowed to talk about their existence or about what was gathered or who was the target, even to the target him- or herself, under pain of prosecution.

This is no stretch of the Fourth. I suggest you read the whole of the link I posted.

Regards--
Mary Anne