This is news to me, and I would think would be a great cometitive disadvantage. There are already airlines which are "dry" for ethnic reasons, and they do have a problem. PIA will allow you to take your own, and they will serve it - discretely. BA will serve you drinks free, but will keep an eye on how much you are drinking, and although it is subjective judgement, decline to serve you if they think that you have too much. Duy Free sales are such a money spinner that the carriers would have great difficulty in stopping people bringing alchohol aboard. Sad to say, but I suspect that any reticence in serving doubles on International is more to do with dollars and cents than flight safety.