Much the way Stafleet is not considered part of the military.
That particular convention changed for naval forces during the early 19th century when it became impossible to ignore the fact that professional military sailors were always going to be superior to -- for lack of a better term -- armed maritime volunteers.
Starfleet hasn't gone through a similar transformation to "professional combat service." Far from it, they've actually figured out that their skill as scientists and engineers gives them the advantage over other forces that specialize primarily in combat. Which makes a certain amount of sense; a crew of humans is never going to out-fight the Klingons in a military struggle, but they can out-think and out-tech them any day of the week.
Just like the word "navy" literally means "group of large boats."
The Enterprise may sometimes behave like a submarine (much to Scotty's chagrin) but it is not a boat.
I'm basing it on the fact that the primary purpose of Starfleet, as stated over and over again in every series, is space exploration and diplomatic contact. Military and law enforcement are secondary roles.
The Federation is an unusual organization.
So there's no real call for the insistence that a non-military organization can fill a military role when it needs to. We both know that, REALISTICALLY, this would not actually work as such an organization would lack the clarity of purpose and the necessary ruthlessness to actually participate in a war. The fact that Starfleet is not a military organization is therefore UNREALISTIC on a lot of levels, but no more so than warp drive, transporters and deflector shields creating a thin bubble of energy that depletes by percentages whenever they're hit.
And NASA is not a military organization. See how that works?![]()
@The Old Mixer already reminded you not to do this. Please consolidate your replies into one post.