Manual safeties on guns designed to be ready to go with a hair trigger (like a 1911 or an AR) are necessary. Not so on revolvers, though. Same for striker fired handguns, like the S&W M&P Shield Plus.
It takes less trigger pull to fire a round from most striker fired pistols than it does on the average two stage Ar15 trigger. A mil spec AR15 trigger is anything but a hair trigger.
