I have no problem with someone lending a friend a mix CD (or MP3-CD-ROM) of their favorite music to allow their friend to try it out if, within a reasonable length of time the friend either returns the CD, destroys it, or buys the music for real.
I also have no problem with someone who privately emails a friend an MP3 file of some favorite music, with the caveats noted above. To be sure, the person would have to take the friend at his word as to whether he destroyed the file or bought the music, but someone who sends a reasonably-trustworthy friend a file under such conditions can be said to have made a 'reasonable effort' to ensure that it was not abused.
By contrast, anyone who makes a file publicly available for anonymous download must be well aware that it may be downloaded by unscrupulous people. The act of putting up a file for anonymous download without permission from the copyright holder represents a wanton disregard for that possibility.
In many cases I have no trouble with people who download music to sample it, whether legally or not, if their own use of the music is limitted to such purposes. I can see no excuse, however, for people who promiscuously make copies music available to everyone without the consent of the copyright holder.