Most Green Day doesn't even sound like punk these days, let alone act like it, but when they did those two songs and I watched the video, it came across as punk, not just stylish posturing, that's all I'm saying. I had to see what they acted like live to get that sense. I'm not really a Green Day fan, I just feel that if you could separate those songs and a few of their other recent ones (NOT "Boulevard of the Soccer Mom Power Ballads" obviously) from their context as hit songs, and imagine them with grittier production, they serve the exact same purpose as any punk served in the late '70s. and maybe they're calculated pandering but that's impossible to judge. I'm not an expert on what is or isn't punk, but this my rationale:
1. punk=defined by rebellion. a supposedly anticapitalist band such as Pink Floyd can sign to a major label and maybe be seen as hypocritical on a personal level for doing that, but the purpose of their message is not just rebellion, they attempt to be a bit deeper (not saying they actually are), so it doesnt completely invalidate what they are doing. this is why Rage Against the Machine sort of runs into credibility problems, as a band with the punk style approach but on a major label.
2. that kind of brutally honest approach seems faked if coming from bands like Green Day or RATM, just due to their position in the establishment. so technically you cant be punk if you join the establishment. it's simply the opposite thing.
3. BUT, these days there is absolutely no opportunity to get music heard by the non-musically-aware age range punk can actually have a big influence on, without joining the establishment in some way, whether that's being distributed by a major, doing a commercial, some shit like that. and regardless of if people think they were bandwagon jumpers, or if they sucked, no one says the Sex Pistols were not punk. the Sex Pistols were on a major label.
Don't get me wrong, I would be glad if no one ever talked about Green Day again. They are one of the most overexposed bands in memory and what they do is . Calling "American Idiot" a punk song is kind of like calling Interpol albums post punk. They are both latching on to previous movements and feel too late and too retro to fully convince you, but they update. obviously punk is more of a sensitive category for its fans than post punk, but if you look at the way Green Day has been able to get people across America to listen to a hard rocking (albeit super-overproduced + guitar solo) song which says "maybe I'm the faggot america," I consider that a punk act.
So, is Green Day a punk band? Yes. They write power ballads, but they also write punk songs, the way Interpol writes post-punk songs. In the case of Interpol this means taking a retro sound and mood and writing songs that update it. In the case of Green Day this means taking a retro sound and subject matter and writing songs that update it.
Are they "punk" as an adjective? The way everyone ranging from Bjork to even possibly U2 could have been described at one point in their career or another for doing something daring and fucked up and rebellious? Hardly hardly ever.
My favorite punk song lately is the Adverts' "Great British Mistake." But I dont really listen to punk much so maybe I should shut up with the generalizations.