One of those things is not like the other things (it's the one where you build things that are explicitly designed to kill human beings). Not sure if you were calling that the coolest work, I certainly wouldn't call it that.
There's nothing wrong with building weapons for defense. It's arguably the entire purpose of nukes at this point.
Even for offense, other countries are working hard to build out their arsenals.
I'm personally fine with building AI weapons, for example. If a contract opportunity appears, I might take it. After all, where else are you going to see the most advanced weaponry in the history of mankind?
That is absolutely not true. There are people in the governments of every nuclear power would use their weapons aggressively given the chance. That's why policies of disarmament are so necessary. As long as humans have nuclear weapons the probability of practically annihilating our species and leaving any survivors living in the stone age again remains higher than zero.
Nuclear war is the single biggest existential threat humanity faces. We can deal with pretty much anything else.
I really do feel that reasonable people need to join such organizations, though, otherwise only unreasonable people will be in them. I recently found (to my dismay) that Von Neumann argued vehemently in favor of bombing the Russians before their nuclear program could be built, and all I could think was "This isn't the type of scientist that should have a lot of influence."
I just wish it wasn't like this. I wish we didn't have people engaged in the business of enabling industrial scale murder. I wish it wasn't profitable. I wish the citizenry would see through the propaganda and hold their leaders to account. I wish it wasn't the nation's poorest who were sent to die for the benefit of the nation's richest.
The war machine is a rotten, gruesome system, and I acknowledge it's not going away any time soon. But the least we can do is agree not to actively contribute towards it.
I am strongly in the 'we only need to defend American soil' camp. I'm not sure how much that costs, but considering we're a nuclear power, we have two relatively friendly neighbors and thousands of miles of ocean between us and our nearest peer enemies, it wouldn't surprise me if we could get away with spending a miniscule fraction of the 700B we do today.
Is that a good thing? I’m not so sure. The age of mass armies was also the age of democratisation. If war is waged by defence firms and brilliant technocrats, then maybe defence firms and brilliant technocrats will run the country.