During my dispatch days, I never had a problem off loading anyone. Infact I used to enjoy it.
If I happened to be at the gate and saw what I thought to be a drunk passenger, I would have a casual conversation with them about their holiday. You can usually tell if they are drunk when chatting to them as they stink of booze and tend to be a tad on the unsteady side. From there I made a decision to either allow them through the gate or take them to one side and get a second oppinion. If I did allow them through the gate, I would follow them down to the aircraft and make them known to the crew. They could then say if they would be happy to allow them to board. If I stopped them at the gate then another senior member of staff or the number one would be called to give a second opinion. Thats what I used to do.
I did find that some of the temps did not like dealing with irate passengers so would pass the buck to someone else (ie. The crew). As I said above. I had no problem spoiling someones holiday just because they thought it started in the airport bar.
I do think that there should be system where a boarding card gets stamped every time you buy an alcoholic drink at the bar. After 2 stamps you are only allowed soft/hot drinks. But this wont happen because the airports make big bucks from selling booze.