People generally hate on "noobs" because of their own lousy self esteem. They use the whole "I've been here longer then you, so I am instantly smarter then you" approach when trying to argue with a "noob" who is smarter then them.
Also, most people who bash on "noobs" probably get beat up in real life and then take out their frusturations by picking on new members to a website. Since they can't do it in real life they try to redeam their own crappy self esteem by putting people down online. They tend to think they're tough shit, untill they get their lunch money stolen in school the next day.