*Sigh*... All right, I understand your point of view. They're not your acquaintence, they're not your concern, and I certainly see how approaching a severely drunken man in a bar is a shitty idea in the line of... arguments. But you can still report the license plate to the police. It's not stepping in unjustly if someone's life is at stake, which it always is when people drive drunk.
Quoted for emphasis, spot on. This reminds me of the bystander effect. I will simply never understand how anyone could walk away and decide he/she has no responsibility in such a situation. I would never sleep at night if I knew I could have made an effort to do something but chose not to. I think that's the point here: in the example of someone about to drive drunk, it requires minimal effort to pick up the phone and call the police, at the very least. There is simply no good reason not to do so.
HM: Very visually noisy, your face. It's like a brass band under a wig, marching towards me every day.
^My thoughts exactly.