Skylark - I agree giving passengers large quantities of alcohol does not help if they are showing signs of being disruptive. Unfortunately alcohol is not always the cause of aggressive or strange behaviour, and passengers do not have labels to tell us they are about to go beserk or that a simple thing like not liking the film being shown is enough to tip them over the edge.
I was on the BA2069 Nairbobi flight in which has been well documented about the behaviour of the passenger who nearly crashed the plane, alcohol had no part in that incident.