Historical View of Metal Music
Popular music was recorded and marketed as a Counterculture which opposed the normal, functional, and unexciting Culture that was dominant in society; by being outside of that which was in power, Counterculturalists argued, they were able to see what was "real" and to implement a "progressive" worldview in which moral correctness brought us gradually closer to a utopian state.
This marketing mirrored the process of adolescents, the main audience for popular music, who first reject the world of their parents, then once independent re-assess their own values, and finally, rejoin society on the terms of these recreated values. This determines "reality" as they will act to create it, based upon their values system.
While dominant Culture sought what was pragmatic, and Counterculture pursued the moral, metal music became its own movement because it could not agree with either of those approaches, preferring instead to try to seek what was "real," or meaningful and "heavy" (in the LSD-influenced vernacular of the time). Their approach did not aim at correctness, but assertion of subjective meaning.
For detail read here : www.anus.com/metal/about/history.html