If you get drunk and get behind the wheel of a car, it's the same to me as walking around with a loaded gun and firing randomly. Does it matter that you didn't set out to shoot someone?

Unfortunately, this is not the case. You still are conscious of your decisions when you walk into a bar and fire randomly. There is a reason its considered rape if you have sex with someone who is intoxicated; they can no longer provide consent. The no longer have the ability to reason for themselves.

Are we going to argue that you're a murder if you drink to excess while your keys are still in your pocket? Because that's when the decision was made, not when you get in your car drunk. At that point, its not you making the decision.

"At that point, it's not you making the decision."

Well, no. Turns out that alcohol's effect on behavior is strongly dependent on culture and/or expectations:

http://www.sirc.org/publik/drinking3.html#_VPID_5

Of course! One is murder and the other is criminally negligent manslaughter.

And why the hell should intent matter? It's the outcome that is relevant. My grandfather was killed by a perpetual drunk driver. I don't give a shit what his intent was, he obviously had no regard for the safety of the innocents he was putting at risk. He deserves to rot in prison.

repeat offenses should be factored in to sentencing and charges just as much as intent. regardless of your particular situation, our legal system (and most) have the concept of intent built in (manslaughter vs murder, etc.)