Some metal fans are like that, but about people like Michael Jackson.
A lot of people have seen a general rise in popularity of true metal over the past few years, especially during the new millennium. It'll crest like a wave, then die back down whenever something else comes along. Time is the best test; some of us will still love metal years from now when the next thing has arrived and we'll be laughed at and dismissed all over again.
It IS genuinely irritating to see new people, especially younger kids, jump onto a bandwagon they either mocked two years ago or were unaware of two years ago. It's sometimes hard to control the knee-jerk reaction starting to dislike a band because you don't like their fanbase turnover, but that's life (i have this problem). A lot of times, new kids don't know the whole history of a band, or they haven't "been there" since the band's humble beginnings. If they care, they'll learn, and if they don't, then they'll be gone tomorrow.
I remember the very first nu-metal kid in my town, way back in the 90s, when Limp Bizkit toured before they had a record deal, when Korn was just a curiosity in a few kids' CD players. The term nu-metal didn't exist yet. He was the "real deal" back then, and was really looked at as an outsider, a "freak" of sorts among kids at my school. Fast forward 3 years, and of course we all know what happened. I kinda felt sorry for that one kid, because he was there before it was cool, and after a while people who didn't know him were passing him off as just a trendy, faceless nobody who was riding a fashionable bandwagon when in reality he'd been one of the "true first."