Eddie, remember Trek was based on the age of sail. Navy ships not in well charted waters explored whenever they weren't actually involved in other missions because there was so much unknown about the world. So that argument doesn't preclude them being a miltary. And, just because the Macarthur was a military exploration mission does not mean Starfleet has to follow Niven and Pournelle's lead on how it would operate. Different writers, different universes. Sparta grew it's empire out of the wreckage of the corrupt Co-Dominium, which stamped it's attitudes and development differently.
This whole resistance to Starfleet being a military was an inane grafting in TNG, and I believe it grew out of hippie protests in the 70's calling soldiers babykillers. Roddenberry should have made the point that Starfleet was a better military than today's, instead of repudiating his own service and making ridiculous assertions that fly in the face of logic. And sadly, many who grew up on TNG instead of TOS have bought the idea.