Well, to add to your side:

One could have mentioned the fact that most pirated music is not a lost sale in the first place: Although this kind of survey is probably not very accurate, the vast majority of people said that if they didn't pirate it, they still wouldn't have bought it anyway.

Another angle is the fact that most mainstream top 100 songs are played on public airwaves almost constantly, so downloaders are simply getting an otherwise free song from a different source, making it just a devil in the details.

You could also argue that you're downloading one song out of an entire album. However, this argument would be countered by me asking if you only want a portion of a product, is it ok to steal just that portion? Also, the point has lost its potency now that most songs on legal download sites are sold individually now anyway.

Finally, I'm surprised nobody brought up the production costs of a CD (less than 50 cents). Although that point can be countered by the fact that it is the intellectual property that is protected and not the physical property, it could be argued that the artists and all the middle men get their fair share long before a record goes platinum.