The argument depends on what exact piracy you are talking about, and even then it varies wildly with the situation.
For instance, in the case of music from big-label record companies, the artist makes maybe a quarter off every album sold--the rest goes to pay production costs or into the executives' pockets. If I want to support the artist, I go to their concerts and live performances.
For movies, my logic is that if I paid to see it in theaters ($10, which is generally the same as the dvd, but I'm not sure since I haven't bought a dvd in ages) then why should I pay to own the dvd? Generally, half the movies I pirate I wouldn't see otherwise, so when I talk about it to my friends I'm essentially giving them free marketing.
Most programs/apps that are good are freeware; the few that aren't are retardedly overpriced (several hundred dollars for photoshop, for example). Anyone short of a professional working in said field cannot afford to buy them.
As for games, that's generally the only situation I try NOT to pirate, in part because multiplayer is worthless when you pirate. But they're just so damn expensive, especially for someone without a job.
For an explanation about the whole "money" logic:
I paid $20 for Counter-strike: Source off Steam. I've played it upwards of 500 hours over the past year or so. So, going by those numbers, I'm getting 25 hours of quality (albeit rage-filled) entertainment per $1. For a movie I go to a theater for, I paid $10 to get in for 2 hours of entertainment...that's 12 minutes of entertainment per $1. Why should I have to pay for the DVD when I already paid to watch it in theaters, an experience that is 125 times worse in terms of cost:time of fun.
This post has been edited by Sixty: 01 December 2008 - 01:53 AM