In the mid and late 80s, my metal epicenter, no one talked about the Beatles, Steppenwolf, Led Zeppelin, the Kinks, Blue Cheer or Jimi Hendrix as being metal. KISS was a glam rock band and if you know much about the origins of Casablanca Records and KISS and all the bullshit attached to that band becomes a much larger pattern of behavior and their tenuous metal status.
But I digress, I do not think that there is any need for you to bring your political bias into this, even though this would provide you with an opportunity. All of the bands above (excluding KISS and Aerosmith :vomit) were hippie, countercultural bands that the people who read Kerouac, Ginsberg, loved the Grateful Dead and wore sandals listened to. This, of course, is a gross characterization to which there are exceptions, but enough overlap for the claim to have sticking power beyond me dreaming something up. Led Zeppelin was a classic rock band played to death on AOR stations and all the other bands were in the regular rotation in varying degrees depending on the amounts of hits they had, but Black Sabbath existed outside these boundaries for the most part and everyone who was into metal (ranging from the Judas Priest, Iron Maiden, W.A.S.P. AC/DC mainstream connoisseur to those into were into thrash, death, black, speed, etc.) was into Sabbath. Blue Cheer, the Beatles, the Kinks, Iron Butterfly, Cream, Steppenwolf, Hendrix etc. were not considered an indispensable part of this universebut Sabbath was an integral part of it.