If anything, that's one of the reasons brought up in _opposition_ to monopolistic copyright laws: piracy is going to happen, legal or not. If you don't release your stuff freely, people will google "___ full PDF" and end up with some badly-OCR'd out-of-date version of your text. If you distribute it freely yourself, you're cutting the middleman out in a way, since by doing that you assure that there's a well-known, authoritative, up-to-date and free source of your work.