Good question, CTA. I’ve been wondering myself. If anyone knows, is it a mortal or venial sin to watch copyrighted material, such as movies or music, on YT?
Maybe it depends on whether or not the copyright holder is being deprived of any income by said viewing.
Their seems to be two extremes: an anarchic opinion that all creative work is public domain, and that recording companies and artists are all part of some evil corporate cabal (and we gots ta stick it to da
man!); and the opinion that all people
other than the recording industry etc are evil thieves who are illegally downloading everything they see and selling it on ebay.
There are some, for example, who believe that if you play your radio loud enough so that others hear it, it’s an illegal broadcast, and you could be sued; the assumption that anyone who buys blank CDs or DVDs or (in the old days, anyways) cassette or VCR tapes was a heinous criminal hell-bent on pirating away poor Metallica’s hard-earned pennies – which is why in Canada we pay a surcharge on recordable media.
To me, it’s very grey – and I think each situation is different and must be judged on its own merits, factoring in what copyright is supposed to protect, freedom of speech, fair use, what exactly constitutes intellectual property, etc.
I have watched some stuff on YouTube – mostly snippets and outtakes from TV shows – that, although copyrighted, may or may not fall under fair use. I don’t know. I have also watched videos that have prompted me to buy an artist’s CD – I see the video in that sense as being a commercial for their product.
To answer your question – which I have studiously avoided doing up to now

– I don’t know

. You’d have to make a case that it was sinful in the first place, before judging its degree. Then, of course, for it to be mortal, it has to fulfill the criteria (intent, grave matter, etc).