1) Free speech is not absolute. Never has been. Never will be. You cannot plagiarize, libel, slander or threaten someone with their lives (especially the POTUS). You cannot yell "FIRE!" in a crowded theater. You cannot infringe on someone's copyrighted work. And thanks to Miller v. California, obscene material is also a no-no.
2) The American Library Association specifically forbids the prohibition of any kind of material from someone of any age. Even the most vile. Coprophilia, necrophilia, bestality, the ALA believes a six-year-old child should have free, unobstructed access to such things.
3) Any reasonable law passed by Congress that would have placed responsibility on website providers by mandating reasonable safeguards to keep away minors (e.g., no access without a credit card) has been promptly challenged by the ACLU and the ALA for reasons already stated herein.
Instead of working alongside filthy sickos, you should be working to destroy them. That is what Plan2Succeed is trying to do, and that is why they have my full support.
There will always be filthy sickos out there. If you are really concerned about what someone does on the internet at your public library, maybe you should work to get rid of the internet in your public library. It's better than filters (censorship)
Now, if you want to start your own internet cafe and have filters, that is your own business The marketplace and the quality of your coffee will decide.
Which doesn't do squat about foreign websites anyhow. US based "naughty" material is but a tiny fraction of the whole.