Bashir shooting and murdering unarmed beings is wholly out of character.
Putting his weapon on the 'stun' setting was too much trouble for him? He had to expend too much effort? Also, he killed during his endgame, so the victims waking up and alerting the authorities was not a concern.
His actions robbed his victims of the chace of being saved/saving themselves - for no reason at all.
have a gratuitous
quality to them that completely contradicts his character as established in the series.
His actions are at exactly the same level as Section 31's: making 'tough decisions' just because one can, not because these decisions are necessary. By his killing, Bashir completely sabotaged his position towards S31, as established during DS9's run.