A lot of the "Starfleet isn't a military" stuff sounds like a lot the semantic double-talk about the Japanese Self-Defense Forces (the eighth best funded government armed force in the world) isn't consitutionally and legally a military. The relevant portion of their constitution reads:
ARTICLE 9. (1) Aspiring sincerely to an international peace based on justice and order, the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes.
(2) In order to accomplish the aim of the preceding paragraph, land, sea, and air forces, as well as other war potential, will never be maintained. The right of belligerency of the state will not be recognized.
I think the key point - as in the bit is entirely true is the bolded part. Which to me translates as "we promise not to start any fights, but we don't promise not to fight back".
Which sounds pretty much like Starfleet RoE, and I think given the antipathy between the Vulcans, Andorians and Tellarites and the implied devastation of both Earth's WWIII and the Earth-Romulan War (it certainly was in TrekLit) I can definately see the Founding Members inserting something like that in the Federation Charter.
Legally, I believe that (despite using military ranks) JSDF personnel are classed as "special civil servants" which IMO translates to something similar to "government agent". Hence my previous question re: is Starfleet a government agency?"
BTW, internationally, the JSDF is classed as a military, not a paramilitary (in fact, like the DoD's armed forces, they specifically avoid involvment in law enforcement).