^Community reference
I think you hit it on the nail. What makes some people uptight about Green Day being punk is not the music -- because objectively, punk's pretty much on point. It's the fact that they were wildly successful. Can't be punk any more when that happens.
Whether or not an ethos espousing rejecting authority should be applying authority on what other people sound like is another matter altogether :)
Their Keurig "partnership" might suggest otherwise. And it's not just because they've partnered with a huge corporation. But mainly because their coffee company - "Punk Bunny Coffee" - puts a huge emphasis on "sustainability". And while Keurig says sustainability is important, their actions suggest the exact opposite.
The term is loose enough to possibly refer to making the business (not human life generally) be sustainable, though the green[day]washing angle is more likely.
Alternative take: punk, as enjoyed by the connoisseur, sounds terrible to people who don't like punk, which limits its success