Example.
I submitted here to HN a link to a PDF which is copyrighted. That has been uploaded to scribd without acknowledgement. When I contacted scribd to ask them to take it down they said it was the responsibility of the copyright owner to make a formal request for takedown.
Who ticked the box? I certainly didn't. Who checked that the person ticking the box had any right to do so? Scribd certainly didn't.
Scribd make no effort to ensure that copyright is not breached. There is no traceability. Their "efforts" are ineffective and insufficient.
Someone made a comparison with ISPs. The difference is that if I host material in breach of copyright, my ISP can cut me off. Getting back on is a pain, and costs money.
If someone uploads material to scribd in breach of copyright, there are no sanctions, there is no culpability.
It might be legal, but I believe it to be immoral.
I'm repeating myself. Perhaps I should shut up and go away before I get really angry.