Funny how many of the "more free" states have more restrictions on where one can carry than imposed on subjects of the DPRM.
The source of many of these bans is confusing "drinking and guns don't mix" with "liquor licenses don't mix". The difference between the two is considerable.
Nice in theory but, in practice, that ranks right up there with "you don't need to fear conviction if you are innocent".
First off, there is no standard for the crime of carrying under the influence in MA. It's not like OUI with a defined limit (yes, I know that you can theoretically be convicted of oUI with a lower BAC, but in practice the magic line is .08)
Secondly, you can be assured that the fact that you shot someone "after drinking" WILL be mentioned, and emphasized, in legal proceedings. If you didn't have the foresight to get a blood test for BAC, at your own expense, after the incident (assuming you were out of custody soon enough for the BAC to be reliable) you can be reasonably assured the prosecutor will allege that you were drunk - especially if it is a clean shoot. The goal will be to shift the perception from "lawful shoot" to "drunk shoots someone".
The alcohol card can even impact the type of plea bargain you get offered. The weaker the case, the better the deal.
Think you won't take a plea? Come back when your attorney has said "It's a no jail time deal, you'll be a felon for life, but the $25k you've paid me so far will pretty much cover it. If we go to trial, I'll need another $75k, and you're assured of serious prison time if we lose.".