
Quoting
Taxing Matters
The public does not have a right to access all public places regardless of circumstances. The government may ban persons from government controlled places for a variety of reasons. One of those would be for the safety of others visiting that space. So if the library has determined that this person may be a risk to another patron it may legally bar him from the library. You don't know that it was simply the librarian that made that call. It might have been, for example, the library board or the chief executive in charge of the libraries that made the decision. You also don't know what information the library personnel had about this person — you don't know the details of the complaint nor do you know what other information the library may have gathered. In any event, if he disagrees with that decision he'll have rights to appeal the ban.