There is no crime watching something you don't know the copyright of, doi, it's important they will make it important..maybe.
I forget now. Oh yes, because it's there everyone can watch it. If you don't watch it at all, you might be out of the loop. Those videos would have been taken down if it were that important. They do say not to post TV shows. They even took down my Mucinex pills commercial a few years ago when Twilight was in its younger days.. However, I do post myself dancing online to any track. I figure that the quality isn't good. I mean, it's there. The only way to change the rule is to change the rule. Have people find you another way, indeed, and just post a link to the YouTube video but not let it show up on your profile. I don't bother with that, and sometimes the tracks are automatically taken off and then returned.
I do believe that you should allow this stuff online because you could do it just as easily in real life. You just can't have strangers pay you for it. You can't copyright it as your writing. We are already allowed to sing songs 80 years after the composer dies.