I'll leave it with this: in Yesterday's Enterprise, is Tasha Yar still alive and Deanna Troi not present.
Did you never wonder exactly why that was?
It's because Armus killed her.
More broadly, it's because in the prime universe Riker tells Armus "We believe that all intelligent life has a right to exist," which Armus -- being the sociopath that he is -- immediately latches onto as a sign of weakness. In the alternate timeline, Starfleet does not hold to this belief; they'd deal with Armus along very different terms, and Armus would really have only one way to get under their skin: torture Deanna to death, spit out her mutilated corpse, and then laugh and taunt them when they find out their phasers don't hurt him. That change in ethos isn't just a minor detail like a uniform change or a willingness to pull a weapon. The basic assumptions behind all of their decision-making would be different, their basic priorities would be different, even things so small as the default setting on a security officer's hand phaser (is it stun or kill?).
I think you are fundamentally underestimating the basic implications of a militarized Starfleet when you assume that a simple mission change is all it would take. It would become an ENTIRELY different type of organization with entirely different procedures and practices. Those types of changes do not happen casually, nor are they easy to undo when the fighting's over; indeed, this is an issue that Trek itself actually touched upon in "The Hunted." It's easy to transform a peaceful man into a soldier, but it's not nearly as easy to turn a soldier into a peaceful man.
I'm not going to belabor the point any more because I honestly don't think you're capable of discussing the subject honestly. I think you're disagreeing just to be disagreeable -- again
-- and I don't feel like going through this with you a second time.