However, supporting the record label by buying the discs will make it so much easier for the band to get the funding to go on tour. For the music genres filled with people with a genuine love for what they do and where performing to appreciative fans is the end game for getting into the business rather than money (most genres except the Pop Idol, celebrity obsessed half of the pop music section) this can be its own reward. You can also then further support them by going to see them live and possibly buying their band paraphernalia / crap. Not to mention that discs that sell well encourage the labels to give better contracts in the future.
I'm sorry, but the only justification for pirating music is getting the material that is out of print and unobtainable. If you don't like supporting the record industry, don't give money to the bands that feel it's a worthwhile deal for them to use them to get their music heard and possibly go and play them live. There is in this day and age, after all, perfectly fine free music and it is totally possible to release music via the internet without the middle man. More power to them, but most of those bands aren't doing major tours - they probably don't want to do that, and that's just fine.
You could possibly make an argument for downloading older albums that aren't going to influence the band's current day chances, but even if you're not really doing the same harm as you would by downloading a brand new album, you're still taking away the artists (small) share, the employees of the record label that do grunt work, the owners of the labels (who own the business and have a legitimate right to earn money from their business) and also from the stores that are selling the discs. It's not really justifiable in any way to say copying is right. The internet is a disruptive technology causing us to rethink the value of data, but until that is done and codified into our laws and culture properly, you should respect copyright.
If you can't afford music, then you have other problems on your plate than feeling like you deserve to be entertained for free.