"If the government had left the threshhold at 0.10, would you still think the threshhold should be at 0.08? "
Yes I think the best balance is found at .08.
How about people respect that limit, leaving it where it is, and allow those very resources to be spent on other violent crime?
Applying it to your example, if the jerk that hit you had a 0.15BAC at the time of the accident and a typical weight and metabolism, he would have probably had a BAC of around 0.07-0.09 three hours later.
I would suggest that a better "solution" for that problem than setting the 0.08BAC limit would be to provide a standard means of figuring imputed BAC. If it can be shown beyond a reasonable doubt that the person was driving some period of time before he was tested, and that the person could not physically legally have consumed alcohol since then, then it should be possible to legally infer the BAC at the time the person was driving.
Someone who blows a 0.07BAC three hours after a crash was almost certainly a much more impaired driver than someone who blows 0.09BAC coming out of a bar.