You referred to it as an accident.You are 100% correct.
If it was a relative I would definitely want vengeance. But since I'm not I can look at it objectively without bias.
And I have no idea the type of person he is. He was definitely a sefish, arrogant prick that night - I'll give you that.
But having him sit in a jail cell for x-years doesn't really accomplish much.
Tripping over your own shoelaces is an accident.
Momentarily losing concentration whilst driving, right at the moment the car in front stops, yep that's an accident.
You don't "accidentally" drink a load of beers and then drive at 150+ mph on city streets. That's a decision you make knowing that it's a stupid, dangerous thing to do. He made that choice, let him live with the consequences.
As for what an extended jail sentence accomplishes? Punishment for his actions, and perhaps a deterrent to others. If he walks away with a slap on the wrist and some community service, it tells others that it's not really a serious issue.