Why are ppl on youtube such jerks?

okay so i'll post a comment about someone that i don't likes' video,and it won't even be mean,its just not an @ss kissing comment,the next thing i know my email is being flooded with hate mail telling me how stupid,whorish,dumb,ugly,retarded,slutti… i am.wtf?! theyll argue forever and come up with the dumbest explanations like i'n 'jealous' and i will reply,perfectly defeating every excuse they come up with,but they just repeat the same crap over and over,they don't even think,they think they are right everytime.wtver,but,no one is like that on yahoo,if they are mean(rarely,if ever)its in a jokey way??