"Well the marginal cost of a copy of [some digital good] is 0 so it isn't stealing!"
That argument is actually completly irrelevant.
I took a train the other night, and there were only 2 people in my whole car. The previous week it was packed. Both times I had to buy a ticket at the same price.
If you don't see what that has to do with pirating music (or software, or movies, or TV), then you don't really understand economics.
Everyone compares it to widgets where there is some fixed cost and some marginal cost, and suddenly the marginal cost is 0 so we should be able to have it for free right? Right?
Wrong. The train has 0 marginal costs, and all fixed costs. Whether that train is empty or full, they pay for the conductor, the engineer, the maitanence and the gas. But you are expected to pay for your ride whether you are 1/1000th of the total population on the train or 1/20th. And if you don't pay, you are breaking the law. Stealing services.
Digital goods are things with a high fixed costs (software developers, authors, directors, actors etc) and 0 marginal costs. There are plenty of other things out there with the same economic model and you are expected to pay for all of them. The only difference is that it is far easier to steal from content creators than service providers.
So please correct everyone you see making that arguement. The fact that copying the music costs nothing really doesn't matter. It comes down to dividing the fixed costs by a certain amount of customers, or there simply won't be content creators anymore. Maybe the songs need to be 2 cents each, I don't know, but the fact is there are high fixed costs and they need to be covered somehow by someone. The lack of marginal cost just doesn't matter.