The point of the low BAC limit is to reinforce the message that you don't drink and drive.
No, it's to reinforce the message that you don't drive drunk. And 0.08 is not drunk.
Back in the day, people would go out, get pissed and drive home ... So the position now is you do not go out, drink, and drive home. At all.
Why not? Obligatory Wikipedia link to the fallacy you're using.
But I digress. Let's ignore all of that for now and just play a simple little game. The figures I have seen indicate that the risk multiplier at a BAC of 0.08 is about 2x normal (at a BAC of 0.00). Risk also generally scales linearly with respect to miles driven (at least for comparable driving conditions; city and highway driving aren't necessarily the same).
So, here is the game: I will present you with two situations where there is more or less equal risk involved. You will tell me which situation is an example of someone who poses a grave danger to himself and other drivers, and which situation is perfectly okay.
Situation 1: A guy has 3 beers on a Saturday afternoon and then drives to the store to buy some eggs for Sunday's breakfast. He has a BAC of slightly over 0.08, which is the legal limit. At this level of intoxication, his risk of being involved in a collision is about twice what it would be if there were no alcohol in his blood. This could be easily avoided if he simply didn't drink before driving.
Situation 2: This guy believes that drinking and driving is never okay in any amount, so his trip to the store is made at a flat 0.00 BAC. However, he's a poor planner because a day or two later he's taking the trash out and discovers that he has run out of trash bags, and he has to make a second trip to the same store to buy more bags. He ends up driving twice as far, and the risk is twice as much. This would be easily avoided if he just checked around the house before he left and made a list of everything he needed to avoid making extra trips in the near future.
Which of these two men is vilified as a menace to society?