It's not wrong it's just a bit poser-ish, like if you wear band tee's and don't actually listen to the band then I just don't respect that, be true to who you are, not just to impress people or look 'cool' ..you'll probably create the opposite affect trying to do this. Also, there's a type of attitude you need to pull of certain looks and in my opinion rocker/metal head is that kinda thing. If you dress in rock attire, you'll attract people who like the same style/bands and then when they realize you know f*** all about the bands, you'll feel like an idiot and probably look like one too.
Its like a wolf dressing like a sheep. its a no go for me, its taboo. Its okay as long as you aren't going out of your way to appear to be 'metal', like wearing bamd shirts and such wherw you don't even know who te band is.