system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why don't Star Fleet soldiers get body armor?

I know it isn't standard equipment for most as a sign of good faith with other species and civilizations, but when Star Fleet is at war with the Dominion, why are they as well armored a Napoleonic era soldier?  A metal cuirass looks like it would be better than nothing.
gpt
Phasers (and to a lesser extent disruptors) are *ridiculously* powerful (even a hand phaser can sublimate a humanoid in a single shot when set to maximum power), so outside of exotic metal platings and reactive armor (which is really something you don't want strapped to your chest), very little will actually save  you from a blast that's meant to kill.  Phaser weapons especially are very flexible, with attack vectors ranging from nervous system trauma to a pencil-thin penetrating beam to simply burning chunks out of the target, which means that the current paradigm we use with *ballistic* armor (spread the energy out over a wider area) wouldn't really cut it.  The only possible utility of armor against energy weapons would be that it may force the enemy to up the power slightly, thereby reducing their shot capacity, but that doesn't really seem to be worth the encumberment that armor creates.

Body armor would really only do any good when it comes to (seemingly common) hand-to-hand combat, which is why the Klingons wear it.  But this again ties in with how the Federation, for better or for worse, *hates* appearing openly militaristic.  

Although personal defense *forcefields*(as well as tactical explosives) apparently do exist as of Deep Space Nine, we just *never* see them for whatever reason.  ~~Blame it on the writers~~