So what branch of the military was Christopher columbus. Or in the klingon military how many scientists or engineers do u think are serving on those ships. Not too many, wanna know why? They consider theirselves a military, so diplomacy or scientific discovery is their very low on their priorities. While in star fleet, every vessel seems to be filled with mostly scientists and biologists, engineers. From the top of the chain of command to the lowest ranked. Star fleets seems to essentially be NASA, if they were capable of interstellar flight and warfare. Starfleet will defend the federation if it needs to but its main job would be exploration. Which makes sense if u think of the federation, Starfleet officers keep remindibg us their not soldiers, and i am sure if they were considered the military, new worlds would be less likely to join the federation because of the fear of having a foreign military force superseding theirs. However if they are considered more explorers than soldiers, worlds would be put at ease. Its do clear how different star fleet is in contrast to the armed forces of other factions. Star fleet is essentially armed scientists and explorers with the mandate to use lethal force if they need to.