This is actually a daydream of mine (although it will never come true!)...alcohol being forbidden on board any aircraft, at any airport and no duty free alcohol either (or it would go straight in the hold...what I mean is, not accessible).
I'm not saying that it would solve all the problems, or that all cases of disruptive passengers would disappear but I believe it would narrow it down quite considerably.
Anyway, it will never happen so keep offloading them if you have the chance. I find that you usually only find out in the air if you have someone nasty on board. Fingers crossed, I only ever had one arrested on arrival. That wasn't nice, and I hope I won't have to do it again. Guy cooked his own goose though, and I wouldn't hesitate to do it again if necessary.
Good thread!