You don't encourage the good by propagating the bad. Everyone has heard of metal today, but for most people it has become a spin of pop music, because such people are rather "flat" individuals that don't look for more than what pop music offers. Metal has become increasingly popular, but most of the new metal listeners belong to this group of "pop fans" who bring their drama into metal. Other individuals have potential for an understanding that must be awakened by confronting them with the best music metal has to offer.
Think of a flower.
It offers the bee nectar, and as its payment, makes the bee spread pollen.
We need something to bring in more people. We get popular, and that brings the ones who can recognize the best to us, and then others emulate them.
Most of the good people out there are not exposed to good metal, and unless they suddenly see a vision from heaven telling them what to look up, they won't know.
We should not be antisocial dorks who won't reach out to others. They're our people, they're just "sleeping" right now, and we can wake them up, and do it without telling them they're dumbshits for listening to bad metal. They're not dumb; they're misguided(*).
People are going to look after what they think they want.
We're like a radio show -- we give them what they want, but we also give them what's good, and they slowly turn toward the latter, first personally and then demographically.
In an ideal world, you would be 100% correct.
Right now, you may be more like 49% correct. Do you see what I'm saying?
* - I think many are capable. Some are not. I'm an IQ realist, including its distribution among ethnic groups and the clines/classes within them.