Of course not.
Many people can commit suicide by gunshot wound to the head with 3 times the lethal dose of herion in their system and then whipe off the fingerprints afterwarRAB, I mean seriously.
Now you can call me a durabass (which I think you are for thinking Modest Mouse have talent) and that all and all Nirvana fans made up this theory as a way of defending Cobain's character (especially considering he had a young daugher, and was actually considering to divorce Courtney and take full custody of her) which is personally reasonable to believe, but in addition to that, many people will shrug off any actual evidence that contrasts with the idea of Cobain killing himself (such as the lack of fingerprints on the weapon in question, but then again they never actually bothered to check the damn gun for fingerprints until a month later, and by then Cobains death was already ruled out as suicide) simply because they WANT to believe that he did it, thinking it justifies them to demonize him as a human being just because they are cool and listen to cool music, unlike everyone else who are just posers, lawlz.