I think that's a bit of a generalization. I can hear notes when it comes to BM like early Darkthrone, Burzum, and really raw shit like Ildjarn. And I fail to see how sloppy playing adds "non-musicality" to a song. I feel that a lot of the time, it shows more artistic expression than a lot of the ultra-precise, ultra-produced stuff out there. Stuff like that adds character to it, my friend.
I admit that raw BM is a really rough genre to get into, it took me two years for it to click... but when one does, it actually is really rewarding. At least IMO. :V
I'm not talking about Darkthrone or Burzum (War is the most boring song I've ever covered live but whatever, the actual song is not absolute crap), but the underground unknow local bands which try to sound like them and sound like fucking shit, like a dog being beaten up.
Ultra produced (Dragonforce) does suck major cock most of the times, but not ultra precise (Wintersun, Necropagist, Vader, Sinergy, ...). That does make the music even more enjoyable, or do you think Alexi fucking up a solo or Muhammed going out of the harmonic lines of the song or Vader going out of timing would sound good?
I agree.
But if it's done intentionally..
Sloopy: uncontrolled and fucked up playing. You can't do that on purpose. That's called going off beat or purposefuly breaking the ''right'' melodic lines, and is actually a technique (hard to say if useful or practical though), and then yeah, credit goes to the musician.
The way I see it, I like Varg Vikernes' philosophy on the matter of playing precision.
"The whole point with the musical rebellion was to not make "perfect" albums, to not make music with "this or that" brand of instruments, it was to not go to a particular sound studio to get "this or that sound", and it was to not sound like other bands. A few mistakes makes the music more alive and personal, it simply gives the music some "soul" and originality, so I never bothered to correct anything. The music on the Burzum albums is simply an honest and sincere, unvarnished and clear representation of me. Certainly I am not flawless or without mistakes, so neither is my music."
I call that lame excuses for what can't be excused. I can accept that he wants to do things a certain way because he likes it even if he can do better (I don't understand it but I can accept it), but justifying shitty playing by saying that it adds rebellion to music is like saying that you're going to do the maths for the ultimate economy formula wrong because you're a rebel, not because you can't. Or like if I say that my Paco de Lucia cover is not shit, but that I'm a rebel and I'm doing it wrong on purpose.
About giving the music soul, freshness and originality, that's what is called a live album imho.
If you are expecting raw BM albums and the like to have ultra-precise playing, and crystal clear mixing, you are simply missing the fucking point of the genre by a lot, and really shouldn't even talk about it tbh. It's a rebellion against standard musical practises.
Raw for me is Vader or Slayer or Municipal Waste. Simple lineup, simple production, not many effects besides distortion and in your face kind of music. Not music recorded with the same quality as if you recorded a rehearshal with your MP3 player. I don't want a BM album to sound like Dream Theater, but I want it to have audible quality. Emperor, Burzum, Immortal, ... actually have that (not the clearest sound and by far not my favourite tone but something audible, not harmful to human ear), but a shitload of non-famous so called underground bands sound to me like if they're just trying to set their amps to get the worst tone possible and make the biggest mess possible.
Plus, the thing that bothers me more about BM: what the fuck is up with the tr00 attitude ''let's burn churches down and chase people down the street and kill goats''. What the hell have fucking goats or pigs or whatever done to BM? What has the normal citizen who looks astounded by someone painted in corpse paint walking down the street? I just don't get it, same as with the stupid karate shit on hardcore gigs.
If you want something in particular, I'd never let bands like Gorgoroth play again or do anything. It's ok to do your music and write about whatever the fuck you want, but not beat someone up for the sake of it.
Bands like Emperor, Dimmu or Immortal can stay though. I won't like them, but they just do their thing.
Tl,dr: I ranted about BM, the search for the crappiest sound ever by some BM bands and the stupid tr00 attitude some BM fans have.
I would think that being able to accurately convey your artistic expression through your instrument would be valued over being unprecise in your playing. But I guess you're probably the type or person to adore Picasso's absurd artwork, seeing how that is quite unprecise, or is it? Perhaps it is precise in that it is not precise 
