I agree with the sceptics... exactly who's going to administer breath tests, under what circumstances, and to whom? What limits do you set? Drink Driving Limit? Higher? Lower? Let's get real - there's very little if any correlation between a breath test result and whether or not this person is going to be a model passenger or not...
Why do I get tested but not this person? Your kids can fly, but not you Mrs Jones... Picture the scene - you've checked in two hours early, for a flight that's two hours late, wrestled your way through the mess and stress that masquerades as an Airport, and you've had three or four drinks while you're waiting... then they turn round say you can't fly... there'd be riots at the Gate - all neatly passed on to the Crew.... and not to mention some very empty Business and First Cabins...
Warn 'em on the ticket, control 'em in the cabin, and charge 'em to the fullest extent of the Law...