Well it's tacky as hell of course, but it's a free market...
Personally I think that kids going around wearing CCCP t-shirts with the hammer and sickle is far worse, considering the 10's of millions of Russians who were slaughtered. They might as well cover themselves in swastikas. And then of course you have the Che Guevara t-shirts, because murderers are très chic aren't they.
But this Cobain suicide note design...yes it's in poor taste but then again people are quite comfortable wearing crosses to symbolize the thing that Jesus was nailed to, is that really any worse? Maybe in a few hundred years time, this suicide note will be considered some kind of holy document.