it's a catch 22.
drunk driving can be lethal and should be caught and punished.
however, the problem is we have a one size all measuring stick for the entire population. no matter how tall, how old, how much you weigh, how much your liver is stronger/weaker than others - there is just one simple number that if you blow it, you get a dwi.
so on one hand yeah you may catch some actual threats on the road due to their alcohol consumption - you just as may catch someone who is no threat in reality, but fails a one size fits all testing approach.