Because the police don't come to your house and hunt you down just because of it.
Millions of people do it everyday, with the economy being down and people being unable to pay for things.
But it hurts the people who produce the music thus the music industry and so on and so forth(sp?).
I hardly ever rent DVDs... Haha I just use on demand from cox. Not too expensive and you dun have to get in ur car and drive to blockbuster or watever to return it xP or of course there is another alternative: just go on YouTube and watch random vidz xD