Pirating someone else's copyrighted work is stealing. Downloading someone's book or song for free from an illegal site is stealing as well. I don't see much difference. In either case, the person(s) who have created the book or the song are robbed. Their well-deserved royalties are not being paid to them.
Pirating cannot be compared to uploading pirated material. Both of them are harmful and hurt business, but real pirating puts human lives at risk. Uploading pirated material causes financial losses in companies, or so to speak, which is bad but doesn't involve human beings. Also, pirated upload material is not as damaging to businesses as people think.