This isn't a legal opinion but a personal one: people who decide unilaterally for other adults what they should be allowed to read or see are assholes.
My web host is in many senses like my ISP: I don't pay them to editorialize.
In the US there is already a huge and well- (and perhaps over-)funded machinery for investigating and enforcing the law. If the laws are being broken, why not let them handle it? (This has the added benefit of applying the existing body of legal wisdom regarding state censorship.)
If the laws aren't being broken, what's the problem?