We’ve been over this before.
If your conscience, personally, is bothered by watching Youtube videos because you think they might violate someone’s copyright, then don’t watch them.
The reality is that in 99 percent of cases, you don’t have enough knowledge of the law to know for sure whether it’s “illegal” for some video to be up there or not. If a video is up there illegally or in violation of the purported content owner’s rights (which technically is not the same thing as being “illegal” in all cases), the content owner can have it taken down.
In many cases, the content owner either chooses not to have it taken down (often because as you said, they are making money off it somehow, getting a ton of free publicity, etc.), or there is something about the way it is presented that might make it a legally permitted use.
I would be more concerned with the morality of the actual content, given that there is a lot of trash on Youtube. You can rely on the takedown procedure mechanism already in place for the rights owner to remove content they own and have a legal right, as well as a desire, to remove. It’s not really something you or I need to worry about.