For most people, sharing and remixing with attribution and no commercial intent is instinctually a-okay.
Under current copyright law, nearly every cover song on YouTube is technically illegal. Every fan-made music video, every mashup album, every supercut, every fanfic story? Quite probably illegal, though largely untested in court.
No amount of lawsuits or legal threats will change the fact that this behavior is considered normal — I’d wager the vast majority of people under 25 see nothing wrong with non-commercial sharing and remixing, or think it’s legal already.
I’m not sure about this last assessment. I think they consider infringement illegal, but in the same way speeding or jaywalking (in NYC at least) are illegal. The broader point about social norms being out of sync with copyright law is spot on.