Drunk driving, almost by definition, is negligent behavior because alcohol alters your judgment and motor control. There was no intent to harm another.
Conspiracy to commit a crime, however, is a deliberate act with multiple opportunities for one to exercise proper moral discretion.
Half of all drunk drivers drive drunk more then twice per month. It is lucrative to police officers working overtime from federal grants, defense attorneys, insurance surcharges, court fees, DMV suspension and work license fees, charges for jail and community service time, etc to take a "crime & punishment" approach but obviously not sufficiently effective.
We'd be far better off requiring first time offenders for DWI to maintain ignition interlocks for five years ($60/month per car) which would eliminate most repeat offenders. It would redirect the money into a technical control that prevents the problem, not a punitive control you don't care about once drunk...because your drunk.
And of course couple that with continued social pressure not to get sh!t faced to begin with.