Most crimes are judged on "intent" and/or "recklessness/undue care and attention" and the same should be applied here. Fact is that if you get behind the wheel of a two ton killing machine whilst under the influence of anything you're being reckless and therefore guilty if anything happens.
In most cases drunk drivers have no intention of harming anyone, but it's obvious they're being reckless. Problem is that assessing risk is not best undertaken by people who've had a few, so "technically" there are mitigating circumstances. So on the one hand, being wankered is not an excuse for being reckless and they deserve the full punishment the law allows, but at the same time society shouldn't view them in the same way as murderers who plan to kill their victims. They're just sad people who are both victims of their own stupidity and unwitting perpetrators of other people's misery.
There's a difference between stupidity and evil IMO.