I also agree with you. But I personally think that the bulk of youtube users is composed with children and stupid teens, which just want to spit out their naughtiest thoughts, dirty words etc to provoke and see they can type anything impunitely. They have fun in that way, provoking and so on. Also some grew up do that, they just want to "fight".
You shouldn't get nervous for that and feel angry with them, the better thing to do is stay calm, and reply very cheerful and friendly and peaceful, even if they offend you... sometimes I did that, it can be funny! and many of them just stopped to write me but I'm sure I "broke their toy", you know what I mean...and some others apologised, also.
But I know, its quite frustrating as a thing.