People in the US are way too lax when it comes to drunk driving.
If you get caught drunk driving once, you should lose your license forever. Period. If you get caught again, you should go to jail for years. If you get caught a third time, death penalty. This should go for any form of DWI.
That's too extreme considering 50%+ of Americans drink alcohol on a regular basis.
Most of these people drink it in social situations (dinner, parties, etc.).
Our infrastructure is such that you must drive to these social events (not many trains or buses).
Thus, if you drink socially, you are very likely to drive under the influence to some degree.
This amount of influence is highly dependent on your size, metabolism, amount consumed, duration, etc.
Even if you have 1 beer with dinner and drive home 2 hours later, you will be influence ever so slightly.
This is why there are laws that set the limit.
Most people are responsible enough to drink very little. The laws are such that the limits are extremely low (.08 in most states).
I think the laws are fine the way they are and society agrees with me.