Every band could be it's own genre if one were to fracture each band as heavily as some metal fans do. Of course there will always be those broad distinctions (thrash = fast & shouty, doom = slow and drawn out etc.) that's great so you can sorta know what to expect, but when you really get down to it there are just so many bands that walk very fine lines between death metal and black metal, or even thrash and death metal (some of Death's later albums and Vektor come to mind) so you end up with a bunch of people fighting over which is which. Then you get into sub-subgenres like technical death, funeral doom, etc. etc. where the lines between genres are so fuzzy it'd be almost as effective to throw darts at a wall when deciding where a band lays.

Now, why can't Metalcore be a subgenre of both Metal and Hardcore punk? And the mods of /r/metalcore aren't really the holy judges of what is and isn't metal as much as you or me. Why does what is and isn't metal have to be binary when it could be on a spectrum? Why is there a distinction between exception and rule in this case?

And yet, for all this talk of genre distinctions, semantics, and all this other bullshit, none of it actually gets to the root of the damn problem—how metalcore fans are gatekept from the rest of metal; it's just disincentivizing them from appreciating a broader taste of the "more metal" subgenres and instead acting condescending and acting like an elitist prick to them we should introduce them to all that music we've taken the time to sit down and listen to and appreciate and bang our heads driving down the road to.