I have to totally disagree with you on this. I didn't read any other post in this thread so I have no context but why should the bartender be guilty of anything?
They can offer to call cabs,but ultimately can they stop the drinker from going to his car? I dont think they can take the persons keys (especially if its the 300lb guy), so they can call the cops but how long does that take?
Saying the bartender is guilty of selling a drink in a bar is saying a geek at best buy is guilty of selling a computer to a pedophile. Or a gun shop owner is guilty of selling a gun to a guy who goes out and shoots someone. Yes they all have their requirements to check (ID,Credit,Background, whatever) but it is always the customers responsibility to use the item correctly and within the law.
Now this all changes if the bartender sells the guy 10 beers and hands him his keys and says your ok to drive, get out of my bar. But I dont think thats what you're talking about.