As stated in Easy Life #1 way back when, in order to play quality ska, one should be able to, at the least, play their instruments, preferably with skill and talent (i.e. Skatalites, Hepcat). In order to play quality punk, one should be very, very angry at society (preferably for some good reason, not because your dad wouldn't let you get your eyeball pierced). One should be able to play, at the most, three chords and be able to scream a lot (i.e. The Germs, The Sex Pistols). While the two styles seem to be antithetical, they were successfully molded together during the 2Tone era, and have both since been latched onto by disenchanted youth across the country. I'm just guessing, but I'd bet money that there are as many ska-punk bands out now as straight punk bands, and probably more ska-punk than traditional ska. It's just too bad it's mostly crap.
So why did it work in the 1970's U.K. and not in the 1990's U.S.? Because, and here's the key, the Specials didn't appropriate the music of, say, the Sex Pistols. They appropriated the attitude. The sneer, the sarcasm, the snide remark went into their music, not the "3 chords and leave it alone" musicianship. Sure they shook up the sound, but their roots were still grounded in the music of ska, not punk. They were covering "Monkey Man" after all, not "God Save the Queen".
There's also that bit about history. Punk and ska were feeding off each other in the '70's, two sides of the same coin almost. But today, punk is as much history as first wave ska was back then. Without getting into that whole "Punk is Dead" argument, the punk of the '90's is not the groundbreaking, influential, pertinent form of music it was in the '70's. And especially not in America, the country that has gotten it's entire mainstream archetypes by ripping off other cultures ("Rudeboys" anyone? Gangstas?). As much as I may like Green Day or Rancid, they succeeded in the mainstream because they were more pop than punk - they weren't advocating slashing society to the ground, just poking it with sticks a little.
But, you say, what about Operation Ivy? Yes, what about that much-beloved God of the ska-punk community, that 80's anomaly that fused the two forms, slapped some Unity lyrics over them, and formed a movement? Simple. It ain't ska-punk, it's punk-ska. The difference is subtle, but it's there. It's more than just the upbeat - it has to do with the influences. For a better understanding, let's do a side by side comparison:
X - You know what instrument you're playing
X - Fast, straight ahead noise
X - Yelling
Meaningful lyrics full of spite
Top notch musicianship
X - Meaningful, but not spiteful, lyrics
There you have it, 3 to 1. While "Sound System" may be a great punk-ska tune, it doesn't make Operation Ivy a ska band.
So what's the moral of this story? Ska-punk sucks. It's not a viable musical form anymore than funk is. The pieces of the puzzle just don't fit that way. Better to play good punk with ska overtones for flavor, than play ska dragged through the mud with bad punk musicianship. Are you listening Slow Gherkin?