This seems to be a moveable line in the sand.
I've used these converters, nearly always in a situation where I am learning a tune that I don't have, usually to prep for a gig with someone. Even if I do have the recording somewhere, it's usually just easier to grab again when my rig is a laptop, Mainstage and controllers, instead of trying to find it. Then I'll open in a slowdowner if I need to, or loop it in QuickTime. Am I really guilty of something? Sometimes I only need to play the Youtube a couple of times and I'm good to go. Innocent of wrongdoing then? Some time ago, I used a converter to grab the 'hellhound' howls at the beginning of Deep Purple's "Hush" to create a sample. Guilty? Where did THEY get that soundbyte from, for that matter?
I'm not building a music library for myself on the cheap. I can live with myself having committed these transgressions, and there'll be no deathbed requests for absolution.