but, rather, pops, clicks, and squeaks. Are other people so totally unconcerned with the way their music sounds?

Yes. Many of the people using the filesharing apps never even listen to half of what they've downloaded and re-shared. They're only concerned with increasing the size of their collection.

The other problem is that these files are often multi-generation downloaded copies. Sometimes they get damaged in the transfer, and no one checks to make sure that they weren't damaged. So the errors are propogated around the sharing network.

This is the main reason I prefer to make my own MP3s from my own CDs. Morality and legality are secondary concerns for me.