There are a few good metal bands.
Scorpions (w/Shenker)
Early Motorhead
Deep Purple
Blue Cheer
Bongzilla

But a lot of metal is poser trash. Too much of it for the rest to be taken seriously.
At least SOME rap represents a lifestyle based in reality, not some teenage goth fantasy.
So, what if you're in a really great metal band?
You might as well be in a really great polka band, because only a few people will give a rat's ass.