there is and always has been a debate as to the boundary of what IS or IS NOT, Metal.
A lot of bands, even in famous "Metal" Movements, like the NWOBHM, really were on the ragged edge between Metal ( a band like Black Sabbath or Diamond Head ) or Hard Rock ( bands like Led Zeppelin or Praying Mantis). To make matters more difficult, there are bands like Deep Purple or Judas Priest or even the Scorpions who very much wavered between the two form one album to the next.
And some bands, like AC/DC or Motorhead, the bands themselves INSIST they are not Metal, but Rock n Roll.
And GLAM (or Hair Rock, Hair Metal) in general falls right on that dividing line. The media in the 80s certainly was to ignorant to know the difference, and most early Metalheads themselves really could not definitively tell you when "Classic Rock" and "Hard Rock" morphed into "Metal".
To make matters worse.... their seems to be a belief amongst most Metalheads, that to say a band is "Not Metal" is somehow an insult. They have trouble accepting that a favorite band might be *GASPS* just a really good Hard Rock band. Then you factor into the equation the "TRVE KVLT, DEATH TO FALSE METAL" crowd who feels anything without shrieks, growls and blastbeats is not Metal..... and it just gets stickier.
Another factor? Metal, like all music has continued evolving.. so bands that were once "cutting edge" of the extreme, suck as Black Sabbath and Judas Priest, gave way to more extreme bands like Iron Maiden, who in themselves gave way to Metallica and Slayer, and so it continues. Today, you have Gothic Rock bands like Evanescence, who actually put out "Harder and Heavier" sounding music than much of the founding fathers of Metal when played side by side.
So what am I getting at? Their truly is no definitive answer, or universally held concensus opinion. For the most part, I would say most older Metalheads would consider Hair and Glam Bands like Guns n Roses, Ozzy, Warrent and Def Leppard as Metal. Most of the younger, or more extreme Metal fans, would call it Hard Rock.
And you tell me... Play Warrant, or Winger side to side with Evanescence..then tell me which one sounds harder and heavier. See the problem?
Still in all, if you look into the basic premise of Heavy Metal, there are a few distinctive characteristics that usually stand out, such as prominent use of Power Chording, heavily distorted or down tuned guitars, emphatic rhythms, dense bass-and-drum sound, and highly emphatic vocals. But even those things vary.
Simple fact... no two people can agree on what IS or IS NOT Metal.
To me, Guns N Roses, Motely Crue, Ozzy Osbourne and the like is some very nice music. Some very nice HARD ROCK MUSIC. But the very next person after me could just as vigorously contend that they are Metal.
*****Van Halen, Metal? HAHAHAHAHAHAHAHAHA! Ummm... he might haveinfluenced some lead guitarist in Metal bands, but not only is it even more marginally Metal than GnR, but there is not a self respecting Metal guitarist alive that doesn't absolutely destroy EVH and his "Eruption".
@Cigarly... btw dude, I am no way meaning that to mock you or your tastes. I just totally have no use or respect for EVH. Guy was IMO decent way back when, but sold out REAL fast. Just my opinion though.