At a BAC of just .02, people begin to lose the abilities to visually track objects and to multi-task. Some people can exceed this level after just one drink. Most people exceed .02 after just two drinks.
I am not going to judge at what level you are too impaired to carry. I am, however, going to dispute the assertion that a drink or two will not impair you at all. It will.
I choose not to drink and carry.
Excellent decision, IMO
Correct, .02 BAC is where impairment begins. An average adult male (5'9" - 175lb) can drink approximately one beer/cocktail/glass of wine per hour without breaking 0.02 BAC. But it is different for each person.
Also, that level of impairment varies widely and exactly where the threshold lies for each person could be between .01 and .04 depending on BMI and other factors.
Just to play Devils advocate... let's look at other impairments:
Lack of sleep, according to to several published studies, impairs your ability to operate machinery like a motor vehicle to a great extent. Slow motor response, impaired visual tracking, slow reflexes, poor decision making, etc. Would that mean that you should never carry a gun if you did not get at least 7 hours of sleep each night?
How about basic stress and anxiety? These are huge factors in our daily lives and also affect our awareness, decision making process, alertness, coordination and motor skills. Are you more likely to engage in conflict if you are stressed out about life?
Do you take allergy medication? Does it make you drowsy?
There are so many factors to consider, alcohol is only the most obvious and one that we know will affect you at a certain level, medically. For me it boils down to knowing myself and my own limits.
I drink, I carry... though rarely at the same time. Like everything else in life when I am armed it just requires a bit more attention, care and consideration than when I am not.