Genres and Subgenres in music

I'm going to go on a mini rant here.

I have never ever understood why people get so pissed off by people using genres and subgenres. Is it so heinous that some of us want to describe the music we listen to more accurately? Saying "death n roll" or "melodic thrashcore" or whatever is far more descriptive than saying "metal" or even "death metal". When I want to learn about a band, getting specific genre(s) is very helpful and I really don't see why people don't like descritpive genres.

I don't have a problem with sub-sub-genres. I do agree that they're more useful in helping classifying certain bands. However, no offense or anything, but it makes you sound like a nerd when you say that "[insert band name here] aren't death metal! They're extreme-post-melodic-brutal-death n roll!"
 
Mini-rant here;
I despise, and I mean truely despise, bands that create a new genre just to try and seem more extreme than the previous band.
Example: death metal lead to the genre brutal death metal, which is really just heavier, louder death metal. However, this lead to the sub-genre ultra brutal death metal, which is just a little bit heavier. Still OK, there are even some bands which actually fit the description (wormed anyone?)
but, today, I came across Ultra Brutal Gore Death Grind. Seems just a bit over the top to me.
I think when bands say "ultra" they are not trying to sound like it's a genre label. It just makes it sound cooler. No one thinks there is a quantifiable difference between ultra brutal death and brutal death. Brutal death is actually distinct from death metal.
 
But where I get lost is there seems to be a lot of negativity towards grindcore, while deathgrind and goregrind are usually considered okay (by my observations at least). Is deathgrind just a fusion of grindcore and death metal, and people can deal with the -core part because it's got death metal influence too, or is the -core influence taken out completely for something like deathgrind, in which case this brings me back to what is grind?

Also terms like "evolution of..." is not descriptive at all in terms of understand a genre. I could say Death Metal is an evolution of Heavy Metal but that would hardly help someone who's never heard of it. And to be honest I have no idea what "Crust Punk" is.

crust punk is basically heavy distorted hardcore punk with a galloping beat, AKA a d-beat. examples include Discharge, Disrupt, Disclose, Warcollapse, Antisect and Deviated Instinct.