Drew,
This isn't really the place to argue constitutionality, but you're barking up the wrong tree. Driving, like flying, is a privilege not a right, and you become subject to the regulation prescribed to govern those privileges. Just as the FAA may conduct an emergency revocation of your pilot certificate in a case involving safety or when it is in the public's best interest, so may a state enact such regulation or policy to govern the privileges extended by that state with respect to a driver's license.
With an annual death toll on the roads due to drunk drivers that exceeds the death toll in ten years of armed combat in Vietnam...this in peace time involving the mere act of driving from place to place in our own country, drunk driving is a terrible, terrible crime for which harsh punishment most definitely should be meted. Personally, I'm all for revoking a driver's license as soon as the driver tests positive, either by BAC, or a field sobriety test...let the driver prove himself innocent or show himself innocent.
When I had an engine failure last summer, a breathalizer test was not prescribed for me. Therefore, I insisted on it. I wanted on record the fact that I hadn't been drinking, or otherwise under the influence. I went to great lengths to meet all the demands and requests of investigators from the various involved agencies.
Like millions of other citizens, I've had the effects of drunk drivers strike close to me, causing death and injury and heartache, and I have zero tolerance for those who will drive under the influence, and every bit as little sympathy for those who will elect to fly under the influence. Likewise, I have no tolerance for the pilot who drives under the influence, but expects to retain his or her flying privileges after such a grossly negligent act. None at all. No more than if one would take the largest firearm in the world and fire it with abandon down crowded streets...that car is bigger than any gun, and the potential to harm much greater on a crowded street.
Cry unfair all you like, but it's far from unconstitutional.
Whereas in criminal procedings, one is presumed innocent until proven guilty, under administrative law, one is generally guilty until proven innocent...it doesn't work quite the same when dealing with a regulatory agency such as the FAA or the State Drivers License Division, as what you may be used to seeing on Law & Order.