Let's attack aggressively
With the difference that fire is more of a physical/natural phenomenon, even when deliberately started, and firefighters don't have to face the same moral dilemmas that soldiers or even policemen face when ordered to take lives. There are no human "fire people" to do battle against, just an inhuman "fire elemental", so to speak.
When signing up for (modern) soldiering or police work, you essentially sign up to be a (relatively well-paid) pawn at the hands of your country's political and military elite and you're expected to do what you're told with much less remorse and "veteran's problems" than a conscript that fought in WW II, Korea or even Vietnam. Know how RTS games work, where you tell your units to go there or do that and they say "Yes, Zir!"? That's all there is to it, really, no matter how much they may pump your head full of propaganda trying to make you feel like a special, super-human pro-democracy righteous warrior.
You are NOT reacting to a natural phenomenon, you're carrying out policy decided by humans, for other humans. There's quite a difference. As long are you're only asked to pump someone full of lead from the safety of a helicopter gunship, sure, it's all fun and games. But if you catch lead in the process, don't expect to find much sympathy outside of a closed circle of people in your same situation. After all, your employer grants you medcare/retirement and probably other perks like citizenship, no?
However, I would argue that war is in fact a natural phenomenon; it is within our nature to be war-like. Despite every advance in civilization, war has always been a fixture in our history. This is what it basically comes down to in your perspective on foreign affairs. You are either a Realist, who believes war is inevitable because of man's nature. Or, you are a Liberal, who believes mankind is not inherently malcontent. I believe it’s not an invention, that it is natural, being a creation of nature like fire. Basically, I made the fire fighter analogy, because no matter what you do, you can't prevent war, like you can't prevent fire.