Okay, here's my take.
Drinking and driving = absolutely zero tolerance in the Marine Corps, period. 0.0001 (or however many decimals a breathalyzer will test to) gets you an immediate DUI if everything is followed by the book. If ANY alcohol at all shows up on it, you're done sir, done.
The Marine Corps also, the last time I checked, had the highest rates of alcohol abuse, underage drinking, domestic violence, domestic dispute, domestic assault, drug use, suicides, divorce, and child abuse. It's a very high stress job, with a high rate of problems that stem from high stress levels.
The other branches may have more violators in number, but, traditionally, the Marine Corps has been the tip of the spear in percentages.
Also, these random breathalyzer tests seem to be aimed more towards Marines who are drinking under age, and drinking while on duty.
I really, very highly, doubt, that they will be randomly breathalyzing the 25 year old Marine who is chilling out in his barracks room on his off time, playing a video game and drinking a few beers.
If it curbs underage drinking, and drinking while on duty (keep in mind, on duty usually always means armed), then oh well, good for them. It does slightly bug me that there even is underage drinking in the military. I think that drinking or enlistment regulations need an overhaul.
If you're old enough to die (17), then you should be old enough for a beer. If 17 is too immature for a beer, then why the fugg are they allowed to fight and die?