Tell that to all those people that can't metabolize alcohol.
But anyway, you said you wouldn't have a drug addict drive a school bus. My answer was: What about an alcoholic?

There is no difference: Alcohol is just as dangerous as any other drug when used in the wrong context and with too big a dose.

Alcohol does incapacitate it's users (yes, it does), yet is legal.

Sorry, you don't have case. Legalisation is still the cheapest way to stop drug cartels.