It is illegal to allow anyone on a plane drunk or drugged up. So it's no god O'Leary and the others complaining about their behaviour once on a plane, their staff shouldn't have allowed them on in the first place.
OK< sometimes it's difficult to judge those who are OK at the gate but go bezerk on-board (depressurisation can affect "normal" people, let alone drunks) but it would help if airports were booze-free throughout the day (maybe no alcohol until 6pm??) and possibly if pax look suspicious, maybe a drugs/alcohol test before boarding, and if they refuse they are simply banned from the flight?
After all we have checks for weapons and dangerous items as we go through security, and if we refuse that then we can't even get to the gate!!