I mean, the guy he was arguing about did call everyone who goes to metal shows fat neck-beards. That's just insulting people, it's not really an opinion on music.
On the subject at hand, the recollections of the OP are about very mainstream bands: Van Halen is enormously so, Judas Priest a little less so, and if you're counting the hair metal bands of the 1980's, they were very mainstream as well. I don't think going to a Van Halen concert puts you in the metal scene persay (I'm not trying to be insulting, nor am I saying you're not a real metal fan, I'm just pointing out that Van Halen's S/T album sold ten million copies. I doubt everyone who ever bought it, or everyone who ever went to one of their shows considered themselves a metal fan.)
The music industry has changed a ton since then. There's no way that a metal song would ever break the top forty on today's charts. Heck, there's barely any regular rock songs on there. Metal and hard rock had a separation (see nu metal), and metal constitutes the more extreme end.
I'll be honest, most people don't like modern metal. The vocals turn them away. The only band I can even think of that I might recommend to an average listener is Baroness, but it still wouldn't sound much like the late 70's early 80's bands (Power metal has clean vocals, but I'm not big on it and don't know enough about it to really make such a recommendation). If you're the type of person who wouldn't mind easing themselves into a new type of music, you might like it. If you want a song to catch you after one listen, there's not much hope.
The thing about Van Halen is that while you're right that they had a good number of fans who didn't listen to anything heavier than Van Halen or Rush, they did also have a pretty fair number of fans who liked stuff like Judas Priest, Ozzy Osbourne, and AC/DC. Also, of HUGE importance is that in the late 70s and early 80s, Eddie Van Halen was the biggest influence on heavy metal guitarists there was, period. The only guy who came close in the early 80s as far as being influential to heavy metal guitarists was, of course, Randy Rhoads.
I think you're absolutely right about the vocals of modern metal being what turns most would-be fans (people who like heavy guitar, bass and drums but want less abrasive, more melodic vocals) away. I also think the number of labels for different styles of metal and then sub-categories of those categories to be extremely divisive. It used to be that if you liked heavy metal and you met somebody who liked have metal, chances were that you liked at least a fair number of the same bands. Priest fans generally liked Iron Maiden and vice versa, for example. And if you liked those bands it was likely that you listened to Black Sabbath with Ozzy on vocals, Black Sabbath with Ronnie James Dio on vocals, or both! If you liked Sabbath with Dio you probably liked the band Dio, and there was at least a fair chance you liked Rainbow. If you liked them there was a good chance you liked The Scorpions, and right there I've listened to the most of the biggest heavy metal bands of the 70s and 80s, not counting pop metal or glam metal.
As for glam or pop metal, there was a big difference between some of the bands. Some of the harder of these bands like early Motley Crue, Dokken (because of George Lynch's guitar playing), and Whitesnake (with a voice kind of like Robert Plant's voice and a heavy blues influence to their earlier music especially), and Skid Row with an amazing vocalist in Sebastian bach and some fairly heavy guitar for a quasi0glam band, were way different from bans like Warrant, Winger, Poison and Bon Jovi and it would be unfair to say Skid Row is no more metal than Poison, for example.
I say the multitudes of categories of today's metal are divisive because even if you do meet somebody into metal, odds are you still don't like many or any of the same bands! Bands the 70s and 80s had a lot of variety but we didn't find it necessary come up with more labels than heavy metal, pop or glam metal, and thrash/death/black metal.