"a medium for sharing our music"

Yes, and we would often learn songs, "riffs", and guitar picking patterns off them.
Were we also "cheating the composer/arist" by not buying the sheet music, their song/tune books etc?

Also, without making excuses for anyone, I very much doubt if artists are likely to make any extra money if their CDs were not made available in charity shops, car boot sales etc. Nor even in the occasional gifting a copy of a CD to a partner or friend.
The chances are that, in 99% of these cases, the recipient would have had absolutely no intention of buying the album in the first place. However, he or she might end up enjoying the music and actually buy the album or, at least, other recordings in the future.

About 30 years, a friend gave me a tape of "The New Victory Band" which I enjoyed so much that I actually bought the vinyl album. Many years later, I bought the CD version. And, of course, I also purchased other music by Pete Coe and some of the other musicians as well as attending many gigs over the years. So they did alright by me, I reckon.