Danger Will Robinson!
If you get into a situation where you must put holes in some jerks lungs the last thing you want is booze in your system.
There is a saying about how every bullet must have a lawyer attached to it. If you have been drinking (and therefore you judgement could be in question) you had best not be shooting unless it is a truly dire situation (and you have sober witnesses)
Stopping power: The power some guns have to make you stop what you are doing and get your wallet out.