I'm not the GP here, but I think the idea is that there shouldn't be a de facto prior restraint on speech for the sake of copyright. By telling the hosts of use

I'm not the GP here, but I think the idea is that there shouldn't be a de facto prior restraint on speech for the sake of copyright. By telling the hosts of user content that they're liable if their users do anything that violates copyright, it would mostly force sites to assume that all content infringes until checked to be otherwise. Even if you own the copyright to whatever you posted, it's not in most site's interest to certify that to enough of a degree of confidence to allow it. I think back to issues Youtube has had in its own attempts to police Copyright, which has led to widespread abuse, and absurd situations like composers being hit with strikes for uploading music that they composed.