This discussion has occurred dozens of times before.
Read the post Danthemandoo linked to - it doesn't just mention illegalities, but a few other reasons why we don't help with it. Furthermore, through experience, myself (and several others) know not to be so naive as to think that when people want to download "music" they are talking about the example you gave - they are talking about Usher's latest release, or whatever. Benefit of the doubt is given where appropriate. We have to use our personal judgement though, because nobody is going to say "How do I download illegal music that I should buy in shops, that might infect me with a virus"
Should we get it wrong (which has happened only 2-3 times in the past), the person will reply telling us exactly what they want, and they will be helped further. 90% of the time though, there's no reply, or they thank us for informing them of the actual purpose of mIRC/IRC.