I mean, there have been at least a few instances of humanitarian missions that actually help, even if there has to be some sort of military justification for it like "building goodwill" or having it combined with some joint military readiness exercise with the host nation. There was that Haiti earthquake in 2021 (and 2010), the relief supplies to Mozambique following the cyclone, Haiti again with Hurricane Matthew in 2016, the Nepal earthquake, that typhoon in the Philippines in 2013, a cyclone in Bangladesh, the Indian Ocean tsunami back in 2004, plus Operations Support Hope, Restore Hope, or Provide Comfort for Rwanda, Somalia, or the Kurds in Iraq+Turkey. I'm not sure you could count Operation Pacific Angel, though it's arguably more helpful in that it's building capacity instead of just giving direct aid, and Operation Christmas Drop seems almost silly I guess (even though sometimes it's medical supplies instead of toys). It's hard to paint those efforts as ultimately about killing people (it's possible though, I might just be ignorant).

Don't get me wrong, there's plenty of nasty shit too, whether it's destabilizing OPEC member nations or their relations to drive down oil prices or just fucking up Afghanistan with no good plan and no real reason, it's not like I'd consider it a positive force overall even in a macro geopolitical sense, let alone the stupid unsanctioned bullshit its smaller factions take part in (and the CIA, as always, can just fuck right off), I just wouldn't characterize "every one" of the campaigns to be about murder.

Most of the expense/time (proportionately) is the Navy patrolling the various trade corridors and oceans with near routine exercises/drills from nearby nations against it, preventing disruptions and theoretically enabling the dying/dead "Pax Americana," ultimately for US capital's benefit (in tangent with the stability of the US dollar as the former de facto reserve currency). It's the real reason the US is content with spending all the money on the military, not just a projection of power but a real return on investment (even more so now that taxes are getting more and more regressive and corps pay less than ever). The murder is almost secondary when it comes to that, a petty demonstration of what they're capable of. Pretty gross tbh.

It depends. You can generally choose a career field to specify in your contract, and you're not directly shooting people for the vast majority of career fields. That's not to say your actions won't support killing people in some way, most career fields are there to support the ones that do, but there's ones in cybersecurity for instance whose goal is generally more aligned to providing support to other nations or industries that might've been hacked. Outside of general areas though, it's not like the mission is decided by anyone other than the U.S. President or Congress (or continuing obligations from prior agreements).