Because unless the sidearms are issued by the unit, they are not uniform. A small number of any unit (e.g. officers, senior NCOs, machine gunners, etc.) are issued sidearms instead of rifles, and can wear them in uniform. Having a "wear your own" policy makes a mockery of uniformity and military training, and reduces a cohesive unit to a cat and dog rabble. If we want a unit under arms, then have its members draw the issue weapons they've been trained to employ, and wear/carry them while on duty - like a military unit.
Should Lt Cdr White be court-martialed?
And when denied the inherent right of self-defense by our own leaders, many, like LCDR White, do the right thing and carry POWs anyway. Frankly, I prefer my Sigma .40 cal to the Baretta M9.
Colonel, USAFR