Why do people dislike YouTube videos?

This is something I've been wondering for a long time.  I watch my fair share of YouTube videos, probably not as many as some, but enough for my liking.  And naturally, I don't like all of the videos that I watch.  But when I don't like a video I just stop it and go on to the next one.  I don't feel the need to hit the little thumbs down button or write some nasty comment expressing my dislike.  Yet I see that people do that all the time.  So I have to ask why?  I could understand if the video was horribly offensive in some way, but most of the time they are just stupid, innocent videos of foxes on trampolines or pandas.  So what is it that people dislike so much about all these videos?  And why do they feel the need to express their dislike so vehemently?  I'm really befuddled by this, especially when one of my videos gets a dislike.  I mean, most of my videos are just useless facts.  I can understand why people might not want to watch them.  They're not terribly exciting after all.  But to hit the dislike button?  That seems a little harsh.  Just move on to the next video.  If someone could please explain to me the appeal of disliking YouTube videos I would very much appreciate it.  I'm just really curious because it doesn't make sense to me.  But maybe I'm missing something, or maybe I'm just old fashioned, who knows.  Either way, I encourage all of you to buck the dislike trend and really make a video earn a dislike.  No more frivolous dislikes!  Something tells me this won't catch on.  But seriously, what's not to like about this video?!