Puritanical nutcases would be my guess.

Or, we could call them non-degenerates.

You can call them whatever you like, I suppose.

Mormons, apparently. They also tend to have good foreign language skills and a willingness to serve. But they represented in the FBI etc to the point it's slightly problematic. The drawback GP is missing is that selecting too heavily from one group can have unintended adverse effects since you lose out on diversity of ideas and approaches - I would absolutely expect many intelligence officers to drink and do other things people might frown upon, because very often the people they need to know and talk to _won't_ be teetotallers or care much about such things.

A lot of people would probably be willing to give up a minor drug or alcohol habit to have/keep a high-paying intelligence job.

I would certainly accept being "always sober" as a condition of employment if the job was one I really wanted.

I can't find the study, but I seem to remember that alcohol consumption follows the 80/20 rule. A small amount of alcohol consumers consume basically all the alcohol, with non-alcholics consuming very little. If you consume very little, it's probably not a big deal just to go without completely.