MEL, I don't like this potential moving responsibility onto airline staff. It is EXTREMELY hard to gauge the level of intoxication of someone you don't know - just ask any staff at the local bar. Some people are visibly affected after two wines, others can sink a hell of a lot yet not show it.
I am not boasting, that would be childish, but in years past i have on many occasions boarded a plane and been served alcohol after consuming an entire bottle of bourbon before the flight. My personality is calm and polite, and I can (could?) "hold my liquor", so never had any problems. But due to this I can fully understand how a group of guys can have sufficient alcohol in them to make them "explosive", but this cannot be reasonably detected before things went "south".
It would be extremely hard for staff to assess this before things got out of control. And as such it is extremely unfair to even consider the idea of blaming them for irresponsible service of alcohol. Many travellers, especially on a flight to a tourist destination, are likely to be in "high spirits" (pardon the pun), so this makes this identification of POTENTIAL troublemakers even more difficult. If some guys were behaving like prats and staff continued to fuel them with alcohol, that would be a different case, but IMHO that is almost never the case.
They should take total responsibility for their actions. End of story.