I'm a free thinker type, but there is a "pubic square" where one's freedom can vioate another's. In other words you can't go walking around in public with your ding-a-ling a swingin', nor should you be able to. While in public, if I or my kids do not want to be subject to seeing someone naked we shouldn't be forced to, either in real life or on a computer screen.
When an adult CHOOSES to pay for a subcription, view porn on his own time or dime, or asks the librarian to unlock the filter, that's different. Having porn laying around in the public square where anybody or their children can run into it does not speak to the better angels of our first amendment.
Besides, if the local libraries are so damned stuck on taking a principled first amendment stand, they can refuse Fed funds, very simple.
So to be sure that they are allowed to exercise the liberties guaranteed by the Federal Constitution, they should have to refuse Federal (i.e., our) money?
Now, I don't think that libraries should be in the business of distributing pornography. I just trust my local librarian a lot more than someone in D.C. on the best ways to deal with the situation.
There is quite a large gulf between favoring local control vs. Federal control over what and how information is to be presented in a public library, and favoring forcing people to see pornography in a public library. Equating the two is invidious.