Yes. My actual preference would be for libraries to use one of the filtering services that actually has humans that can review what is or isn't being blocked and can fix errors as they are noticed. In other words, if a librarian notices that a breast cancer site that looks legitimate is being blocked, they should have a place to send an appeal to open it up, if warranted.
Ultimately, the big issues here for me (beyond the side-track into the legality of porn) is that (A) a library is a public place, (B) children can be found in libraries, and (C) I don't think filters need to be perfect ot be useful. I ultimately agree that human monitors are required and it would be best if parents supervised their cildren. But given the number of children who aren't well supervised and the nature of the porn that can be easily brought up on the Internet, I think some blocking is warranted.