1. GOAL OF TRAFFIC LAWS
The goal of traffic laws is to ensure every single person drives as safely as possible. We of course know that some people can drive better than others, but that does not prevent us from using a single standard. Even if you could drive much faster on the roads and still drive more safely than normal humans (because you are a good driver), that does not mean that you should be allowed to do so --- because every person is required to drive as safely as they can manage, and must follow laws set up for this very purpose.
2. DRUNK DRIVING EFFECTS
We can agree that some people are less affected by alcohol than others, and some people are very good at driving and can drive safely even while affected by alcohol. However, nobody can deny that every single person on Earth can drive safer when sober than they can while drunk. As a result, we can safely conclude that drunk driving decreases everyone's ability to drive, always, and without exception.
3. REBUTTAL OF FOURTROUBLE'S ARGUMENT
FourTrouble's argument hinges on the idea that as long as you drive as safe as other people you should be allowed to drive while drunk. While this might be a good argument, it still isn't perfect. Since the purpose of traffic laws is to maximize each individual's chances of causing an accident, and every single person is less mentally capable of driving while drunk, the only valid conclusion is that nobody should be driving while drunk. This fact should not be contested lest one denies the purpose of traffic laws.
Drunk Driving Licence
Specialized driving and drunk driving are not the same. Specialised driving means you drive a vehicle to the best of your ability. But to drive while drunk means to intentionally make the roads slightly more dangerous. Drunk driving violates the purpose of traffic laws: driving your vehicle as safely as you can. Thus, drunk driving does indeed stick out as an unnecessary evil that should be removed. 10.000 deaths each year are caused by people who thought that this danger of drunk driving didn't matter, and their stories are more than enough evidence to show that drunk driving kills, and therefore we should ban drunk driving.
Unless FourTrouble denies that even perfect driving doesn't ensure a 0% death chance he cannot deny that even an experienced drunk driver is a greater traffic risk while drunk.
No harm?
FourTrouble's logic for claiming that drunk drivers don' deserve punishment is that they neither intend nor cause harm. Yet some people drive recklessly without causing harm and without intending harm. By his logic, they too don't deserve punishment. With us getting such strange results when applying FourTrouble's logic, we can make no other conclusion than to deny its validity. Surely, we don't punish those that actually harm themselves -- we don't punish those that die in a car crash.
Traffic laws do not punish harm, they punish unnecessary increases in the chance of harm --- a category drunk driving falls into.
CONCLUSION
FourTrouble's argument, at least his claim that "DUI laws serve no purpose in our justice system", fails.