THM, there are -fully matured and educated adults- who still debate over copyrights and what is expected, the implications, etc.
This isn't a topic a 12 /14 /16/18 can be expected to grasp to its full extend. Your argument is based on your personal understanding/experiences and opinions/morals and we could sit here all night long over a beer debating it out, but sadly theres is no internet beer yet
Which also goes to say that youtube is clearly doing this for their protection and to try to lower the amount of cases/feedbacks/questions/complaints, it has to deal with.
I should point out that as a 12, i didn't "own" Anything at all. Everything i played with was my parents, i lived in their house, watched their tv, ate their food. Trying to teach me a concept about goods that someone else owns would of been pretty darn impossible, there was no concept of me owning something.
My education was a simple "Don't do this or else you're in for it." Morals didn't quite grasp my fancy t'ill a few years later when i could get away with things but felt bad about them and had to ask myself why. Putting a song online doesn't give you a "bad" feeling, if anything its conditioned to give you a "good" feeling, because your friends are now enjoying it with you, and you're all talking about the same thing and having fun. Then you wonder why its so rampant.
Aslong as the person isn't making money, or isn't degrading the value of what i do, i have no objections to them using it. Use my picture for your youtube music, but it'd better be a good song!