I would quit the band on the spot, if a guitarist said that to me without it being an obvious joke.
It's hard to be in your first band, I just told the guitarist he was wrong and an idiot and played my bass how I wanted. Luckily the drummer agreed with me. Lots of guitarists in heavy/extreme music have whack opinions about bassists; I've been kicked out of bands who felt they sounded better without a bass (black metal/punk, bleah), quit bands who got mad if i stopped doubling the guitar parts, told i wasn't allowed to play in a band if i didn't use a pick, etc. etc. I agree pretty much with Sartori, Death Metal and Black Metal will work just as well (if not better) with a good bass tone as with a bad one. It just takes more work.
That Kurt Ballou recording seminar sounds pretty exciting, where does one find that?