People set up a facebook page. They can then decide if they want to moderate it or not.

People decide to set up a site (not on facebook), let us call it mudcat for example. They can decide to moderate it as they so wish. Would they be responsible for the content or would it be the hosting site?

Do you imagine that all the hosting sites monitor all the pages set up by the users? I doubt it very much.

Why do you think facebook should be treated differently?