They don't, but they do! If the guy was drunk before he boarded, why was he allowed board? If he managed to get inebriated on the flight, WTF were the FAs doing by serving him alcohol? If he managed to consume his carry-on duty free, why weren't the FAs sufficiently alert to prevent the bloke from drinking it? There can not be any excuses for this bloke who surely embarrasses most Australians but there must have been some mitigation strategies available to the crew before the problem turned phugly
All I can say is that you are ignorant of what goes on in the airline you work for.
I can't recall how many times drunks have made it on board QF aircraft undetected by ground staff, cabin crew etc and then created some form of drama on board, nothing like this situation however thats more good luck than good management.
Drunks get into nightclubs undetected, some even drive their cars undetected. some have their own alcohol they poor into a mixer so no one is aware i.e. rum/scotch in with a coke and presto. For all I know it may have been drugs mixed with alcolhol. So CC give him a drink or 2, he pops a pill.................... How do you suggest CC monitor 100+ passengers 100% of the time. You are way out of touch.
Would I be close if I suggested you are an auditor in QF of some form?