When did the categorization of Heavy Metal spin completely out of control?

Metal has become such a huge and diverse genre, that yes those genre classifications are necessary. If you were looking for bebop jazz and you asked for jazz, you wouldn't get bebop. If jazz was a single genre, you would get smooth jazz some swing, some big band, some fusion, etc. You wouldn't get what you're looking for without being specific. The same applies to metal because the styles are so distinctly different, the genre labels are extremely useful for whatever sound you're looking for.

Heavy metal itself has become a genre and is most commonly also known as Traditional metal or Traditional Heavy Metal. It's a sound that encompasses a few different styles but generally is based in a bluesy hard rock. With influence from other genres though, metal itself had to be split into it's own unique genres.

The main general genres for reference are:

. Traditional Heavy Metal

. Thrash Metal

. Death Metal

. Black Metal

. Progressive Metal

. Power Metal

. Sludge Metal

. Groove Metal

. Doom Metal

. Gothic Metal

. Folk Metal

. Industrial Metal

. Drone Metal

Most of the other "genres" you named aren't really genres at all, but rather rely on lyrics to categorize into themes.

Pirate metal, Viking metal, Pagan metal, Christian Metal, Medieval Metal, Funk Metal, and Rap Metal aren't real genres.

Other genres you listed aren't metal for other reasons:

. Nu Metal (it's not metal, it's a heavy alternative rock)

. Metalcore, deathcore and grindcore obviously have metal influence but they're transition genres and take more from hardcore than they do metal.

. Post metal is really just a heavier post-rock and post-rock is such a diversified genre than Post Metal is needlessly redundant

. Speed Metal isn't a genre anymore. It was used for thrash bands back in the 80s before thrash become established as a significant genre.

. Screamo is a genre of hardcore that lived and died in the 90s. Today it's a misused term by scene kids to describe pop metalcore.

I'm not sure what defines alternative metal but it seems to be another form of alternative rock. It encompasses bands like Rage Against the Machine, Tool, Alice in Chains, etc. It seems to take a lot from the 90s alternative sound while Nu metal takes from the naughties ( 2000s ) sound.

I'm going to piss off a lot of people by saying this, but metal fans in general tend to be really hung up on the whole identity thing and tend to sort of be musical snobs. You see, creating these sub genres makes it appear as if metal is far more complex than the series of power chords and pinch harmonics that it really is. It's all about image and what band or sub genre expresses the image the listener wants to portray. There are more posers in the metal genre fan base than all others combined. I have nothing against metal music at all, just making an observation as a long time musician. Bring on the flames metal heads...

The reason for these subgenres is not because they are begging for attention. It's really because there is a necessity for all of these subgenres. Black metal sounds completely different than post-metal for instance. It's necessary. Heavy Metal was a established as a genre a while back, and has gone through evolution. However, I would like to correct the genres that you have listed.

Pirate metal doesn't actually exist. It's just a term used for bands who use pirate lyrical themes. Pagan metal is an umbrella term for bands who sing about paganism. Christian metal fits into the criterion listed previously as well. Mathcore is more so a subgenre of punk. Screamo is also a subgenre of punk.

Now with musical diversity, it is necessary to categorize different musical types in different genres. It makes way for ease of access.

sub genres help when I'm trying to describe a band, or when I'm looking for more of a particular sound, but it's a double edged sword because I think it limits people's imagination, everything has to fit perfectly in a category, but I find the best bands often do not fit perfectly in a category.

some genres are superfluous duplicates of other genres, for example Folk metal is a real genre, as you can imagine it's tradition folk music + metal, but pirate metal is just folk metal + lyrics about pirates, that's not really a genre when you think about it, and neither is Viking metal.

it was about the time that everyone wanted to be something special/different/unique

I try to not think, it interferes with being a retard