I fly frequently and enjoy a drink but the two definitely do not work well together for me. Even a single glass of wine, when airborne, has the potential to cause an intense sinus headache. Two to three drinks will guarantee it. On the ground, only air pressure brings on occasional sinus headaches but nothing like the intensity of air travel that combined with alcohol has on me.

Personally, alcohol makes me a happier person and just overly excited, which is a bit difficult to contain on an airplane.

I do think for some people who can use alcohol to be more relaxed it could be a good thing. Though I'd be cautious about drinking if I were already anxious about flying, since the cognitive effects of alcohol + low oxygen might not be what'd be expected... not to mention the turbulence, babies, and smelly feet I'd already have to deal with.

Presumably because it has health effects that make flying less fun (drowsyness, worse motion sickness, higher risk of blood clots, etc).

I also often have a single drink near the start of a flight.