In-universe, what happened with Starfleet is obvious: the Borg scared the crap out of them. Before the Borg, the Federation thought they were pretty badass, that there wasn't much left to fear out there, that they could do their thing, boldly going and all. Then they ran into the Borg, who shrugged off the Enterprise like it was nothing, and decided that they needed to take a few more levels in badass.
Before Wolf 359, it would seem the Federation was on par with the Romulans and Klingons in terms of military power. Then... they had a sudden immense buildup. New ship designs, new weapons systems. They were gearing up to defend against a threat with a very clear potential to destroy the Federation.
At some point in the future, Starfleet'll calm down and be less blatantly gun-toting. These things are cyclical, methinks.