The comments above about competition are interesting, because the increasing popularity of music and now video piracy points out exactly what the anti-RIAA/MPAA people are saying: that the industries are in desperate need of competition, but as with any monopoly, that's by definition very hard to introduce compared to a competitive market.
What the majority of thes "pirates" are saying is "I like your product, but you are charging far more than it is worth to me. I am seeking a competitive product at a more reasonable cost, which at this point is the cost of maintaining the resources necessary to do P2P." In oversimplified economic terms, prices are set too high, but due to the current monopoly there's no downward pressure. (Or perhaps there is--falling sales--but the trade groups prefer to blame it on P2P.)
Another economic way of looking at it is that there are two seperate markets: people who are willing to pay for a theatrical experience and/or the collectable value of a physical piece of media, and people who care little about quality and just want to see the movie/show in the most convienent way possible, but aren't willing to pay much for it.
In most markets, you'd have different products targeted at these groups--a Honda Civic vs a Corvette, an iPod vs. a $35 portable CD player, or 1st class and Economy class on a plane. But although you could argue that straight-to-video and TV movies are the alternative to the theater, those aren't what the market is asking for, nor are they comperable alternatives. Same goes for TV--people don't like planning their schedules around the TV (hence the popularity of TiVO), or waiting for the box set, so they look to P2P to fill in the gaps.
Basically, the Hollywood and music industry monopolies are starting to sag under their own weight as prices increase due to "production costs" (which should for the most part be lower if actor and mogul salaries had stayed constant, since technology has improved) while quality steadily decreases, and although they've chosen to blame it on piracy, the real cause is selling a product for more than a segment of the market is willing to pay, and not offering to distribute in a form that people obviously want.
This doesn't make piracy OK, but if you look at it economically, P2P is just another market force, and the only one right now that's got any hope of weakening the monopolies in that market space.