Kid of a devil's advocate thing here as I do not drink at all. But as to the carrying while intoxicated, like so many laws they have to be enforced. Yeah this guy was probably tilted but it would have to be:
A) An encounter with an LEO who has knowledge he has a weapon.
AND
B)Thought he was "impaired" (and I believe the language is intentional so the officer can use judgment).
I mean if I go through life routinely violating speed limits but unless I am stopped and ticketed, then I am going through life routinely violating speed limits.* So though we may question his wisdom (or lack there of) he may well be an idiot, no more or less. Perhaps a discreet and gentle discussion may have been in order.
As to drinking while carrying we have the necessary condition above before it can even become a problem. Wisdom and self awareness may dictate a more prudent course but I've known at least one person that, while legally intoxicated was not the least bit impaired as to speech, judgment or reflex. He would decline to drive or ask others to however.
The boogieman of defending a shooting that was otherwise justified but happened while one was "impaired" (like coming out of a dead sleep?) I don't think would be of issue with clear justification. I've seen enough court testimony and exclusion of evidence to know that, if it is not germane to the actual charge probably would be excluded during discovery hearings. Charles would be better equipped to answer this particular point. But if I am "impaired" say at my house and a BG kicks in the door and is left dead in the threshold, then the investigation should easily show that I was justified and that's it. Move the same scenario away from the domicile, add in a bunch of witnesses that see a BG attack you and you leave him dead at the car door...then the same thing. That doesn't prevent a separate charge of illegally carrying or PI from being leveled, but the shooting is either justified legally, reasonable to peers or it is not. If it was a very righteous shoot then the probability of it going to jury trial is reduced in the first place.
How about that fella in Fort Worth who shot the BG fleeing from the officer in the early A.M. in an alley? We dissected that one
ad nauseum and we bantered around questions like what was he doing that late at night, going into an alley in the first place, etc, etc. Was he drinking? I don't know but it is not in any of the available information on the case. Was he otherwise impaired? Same thing. What was he doing out there that late at night, legitimate, partying, mischief? Don't know and it didn't come up. Was he no-billed? Yes. It was found justified by the grand jury.
Now all of that aside, are you more likely to get into a problem if you've had "too much" to drink? You betcha. I would rather no one drank, but realize some do. It is prudent and wise to know yourself and if there is any doubt, keep alcohol and weapons apart altogether. Is it possible one would decide to shoot when they could have done otherwise, while drinking? Depends on the personality but in general I think the answer would be yes. Where that might make a difference is when clear legal justification is absent and then you must rely on how "reasonable" it is...then it might come up and it might ruin your day.
Civilly, if it was a justified shooting, you are protected from civil liability, period. The other factors not withstanding.
*The reference to violation of posted speed limits is intended solely as an illustration and is not to be construed to mean that the author ever violates the law in any way much less routinely
You should feel privileged. 
) About the only time I even drink at home is if I'm having a barbecue and I invite friends over. But even then, 2 or 3 beers over the course of an afternoon and evening is about my limit. Love the taste. Don't like the buzz. I've stuck a 6 pack in the fridge before, and 8 or 10 months later it will be still mostly untouched.
