All due respect, and not trying to be a wise a$$ at all, but who are "the people who are really causing the problems", if not those who are drinking and driving...
You're assuming that "drinking and driving" is an entirely homogenous entity.
It appears to me that the bulk of the actual consequences (major injuries, fatalities) are caused by people at the .20 and above level.
I don't see how prosecuting vast numbers of people at .06 or .07 helps this.