"How does harshly punishing those just barely over the limit, or as can happen, below it, stop these hard core drunk drivers?"
None under the limit should see punishment.
What this accomplishes is equality under the law.
Everyone over the limit should be punished for what they do.
Some say that DUI is harshly punished. I would beg to differ. Many walk away far to easy. Years ago there wasn't even an arrest. Here is my example.
The kid that ran into me was a 2nd time offender at age 17. The very first court date was delayed when I showed up, So were the next four. Upon the sixth the DA came to talk to me and made known to me what the punishment they were asking for this Kid. Fine and probation, that was it.
I posed my discontent. I had my say and they listened to an extent. He ended up with 3 months without his license, 100 hours of community service, 100 hours of drug and alcohol counsiling, fines and a suspended sentence ( I guess that is what its called) of 364 days in jail. He was put on probation till the day he turned 21 and if he violated that probation he would have to go to jail. When he turned 21 his record would be wiped clean...as if it never happened.
When that happened I said " john schmidt...tough on DUI MY A$$! I was escorted by a baliff right out there.
I offer that stopping hard core drunk drivers begins with punishing them early on. What this kid got was hardly punishment (imho).
Jail is the answer imho.
A friend once told me his angle about jail and I agree with him, it goes something like this....
1 Little hammer + 1 Big rock = Lots and Lots of Little Tiny pebbles. ;)
If the guy's BAC was .123 when it was sampled three hours after the accident and he weight 150lbs, that would suggest his BAC was probably around 0.20 at the time of the accident. If you wish to suggest that someone driving around with a 0.20 should be punished more severely than this guy was, you wouldn't find much disagreement.
If your complaint is that this guy, because of the delay in testing, got off because his BAC was 0.123 rather than 0.20, then perhaps you should push for legislation allowing prosecutors to introduce evidence of imputed BAC (i.e. if a person's BAC at some time after an accident implies a higher BAC at the time of an accident, they should be punished for that; the defendants in such case should be allowed to have (and introduce into evidence) tests to determine their own alcohol metabolism rate if they disagree with the estimates used by the government.
What you perhaps fail to appreciate is that while the jerk who hit you got off easy, there are many people whose lives are destroyed for "DUI" convictions with much lower BACs. Correct me if I'm wrong, but it looks to me like you're trying to impose on the non-dangerous people the punishment that you think the jerk who hit you should have received. There's a term for such behavior: "witchhunt".