Okay, Thermopylae does a good job of illustrating why professional soldiers are better than conscripts or militia. But it's not just enough to have a good army--you need to have a society worth protecting. I think we'd be better off if our butchers, bakers, and candlestick makers were more ready to fight to protect us all.
An Athenian voter wasn't just indulging a privilege he'd been handed. He was exercising one of his duties, and he knew that if his vote got the city in trouble he'd be out there with his spear and shield dealing with the consequences. That added a seriousness to political debate that's lacking in today's culture.
We'd also look at each other differently if we had widespread militia training. Right now another citizen is just a stranger, or worse a rival for access to government power and largess. If neighbors are people you can rely on to protect you from invaders, or criminals, you can trust them in other areas, and may not vilify them for having the opposite opinion. That was common in this country two hundred years ago, now it's rare. I think we should try to bring it back.