0.08 level was set in law in the UK in 1967, in France and West Germany in 1970
Most countries have since lowered it to 0.05.
That's the BAC of a healthy male an hour after drinking 2 light beers. That is an absurd limit to set in stone, however there is plenty of evidence to show that /some/ people are impaired at 0.05 BAC.
Ultimately it really amounts to a battle between people who want to operate off fuzzy logic and reasonableness and a people who want to use totalitarian enforcement. There is definitely a significant government-funded (and activist pushed) take where /any/ amount of alcohol /any/ time prior to driving is dangerous, which is obviously stupid and incorrect.
People should not drink and drive, they should not drive while impaired in any capacity, whether its from their prescription medication, a drink, a joint, or simply a lack of sleep. There is also absolutely nothing wrong for a normal healthy person to have a single glass of wine over a steak dinner and to drive home, which will not in any way physiologically impair you.
Driving itself is dangerous. Acknowledging this is obviously smart and correct.
And while I'm sure that you can drive safely at 100 miles an hour, or after five beers, some objective standard has to be drawn somewhere. If the line were drawn at 0.16, someone would no doubt chime in to explain about how they've got it fully together at 0.17.