It is nothing to do with YouTube. This is a symptom of issues the Internet over.
Getting rid of stuffty online behavior starts at home.
I doubt we'll ever see a time where people act civil on the Internet. Forget YouTube, look around on this website and you can find some extreme examples of poor social behavior.
People seem to think being online is enough of a barrier to justify being a jerk. I think you'll find that toxic attitude sinks deep into their real personality, whether they admit it or not.