I think you'll find that outside of larger urban areas in the US, drunk driving tends to fall into a gray area of morality, or in some cases (in my experience, very rural locales with very little meaningful road traffic), an accepted norm.
Almost nobody I know that lives in an urban US area drives drunk or finds it acceptable. This becomes more lax among my suburban friends and acquaintances. For some of my more rural acquaintances, taking a 6 pack along for consumption during a drive is typical behavior that nobody in their community even bats an eye at.
If I'm working in the city, it's easy for me to say "Well, I plan to drink tonight, so I'll cab to the place where I'm drinking so that I'll have to cab from the place after I'm drinking."
When that place is more than a $50 Uber/Lyft/Cab ride away from the suburbs I'm coming from, the options are limited, leaving me to the effort of having to curtail the amount that I drink such that it's safe to drive home. The science I've heard mention is that you can metabolize something like 2 drinks per hour, which is a handy guideline, but lacks so much. 2 drinks of what? 3% Miller Lite isn't the same as 10% microbrews, which isn't the same as 40+% scotch or bourbon. Does that 2 drink guideline cover hard spirits in assuming the worst, or is it assuming the most common scenario of beer? I have no idea.
For me, I tend to prefer drinking at home, or at Uber/Lyftable distances from my home, so that I can be safe, but yeah, everyone's guidance differs slightly, and as someone downthread mentions, relying on choice of drinking safely as judgement is impaired by the alcohol they're drinking is fraught with peril.
This seems like it would work as long as you treat all of them as trending towards the middle of the alcohol content scale (i.e. treat Miller Lite and a highly alcoholic cocktail as approximately equivalent to a shot ). On the other hand I don't think it would work if you treated the ends of the scale as the same (i.e. treating Miller Lite and a highly alcoholic cocktail as equivalent).
As far as 'drinks per hour' guidelines go, that's usually standardized as a single unit of alcohol (e.g. 1 1.5 oz shot of 80 proof liqour OR 12 oz of a macrobrew lager OR 6 oz of a typical wine).
Commonly in parts of the midwest, people will pop a roadie while they're driving, to the point that it is part of the culture in places like Wisconsin and Minnesota.
When I was visiting friends in the US, a totally different picture. Almost everyone was happy to drive after a few drinks and noone did care.
This, I suspect, is the big difference in attitude.
In a suburban area, you have a significant chance of hurting some else when you drive drunk.
In a truly rural area, you are mostly likely to harm only yourself when you drive drunk.
That said, people not having any options to get home ignores the fact that people are heading out to spend money on alcohol to begin with. Budgeting for a cab ride home seems beyond everyone's thinking, in this article...
Cabs at the time you need them for this kind of duty are damn near useless except in the largest cities.
It's only the ridesharing services that suddenly made hailing a ride home from the bar a useful situation. And we haven't had ridesharing services around for that long, really.