Go work for Oxfam, then. Or Save the Children, or MSF, or Greenpeace etc. All the humanitarian work you’d ever want, without being complicit in killing people.
As Cheekyboy pointed out, the Armed Forces have countless capabilities which simply aren’t available in civilian worlds. Similar argument to Cheekyboy, but from an RAF perspective:
The charities above don’t have access to large Air Transport aircraft, so where do they go when they need some? The RAF maintains the capability to get to otherwise inaccessible parts of the world, and thus to reach people who simply can’t be reached by MSF in their Landrovers. They can also respond within hours to incidents thousands of miles away; that’s the reason why, the day after the Nepal earthquake, i was in the middle east preparing to fly aircraft loads of DfID aid directly into Kathmandu. As much as you might like to disagree, there is simply no one else who can maintain these capabilities.
Closer to home, if you are involved in an aircraft crash anywhere in UK airspace (any aircraft, Military or Civil), it’ll be a joint RAF / RN unit which comes out to sort you out. Name any UK aircraft crash in the last few decades, and it’s the Forces who came to the rescue. Baddies put a bomb in a vehicle, and it’s the Forces who come to the rescue. G4S fail to meet their commitments to Olympic Security, and it’s the Forces who come to the rescue.
I understand your sentiment, and i think it would be wonderful to live in a world where we didn’t need Armed Forces. This world isn’t that, and to suggest otherwise is dangerously naïve.