1) Society tolerates a small amount of alcohol for most drivers.
2) Driving while drunk impairs your physical and mental ability to drive safely and only gets worse as you drink more. Obviously a manual driver has slower reaction times than an autonomous system but they are within a level that society tolerates and far better than someone who is drunk.
There are also risks with autonomous vehicles - the potential for equipment/sensor failure, software being unable to adequately handle bad weather, the potential for exploitation by hackers etc.
I'm currently in the process of buying a new vehicle and have been test driving vehicles with various sensors designed to prevent accidents (specifically the Subaru eyesight system). One of my first thoughts was that it would be easy to become reliant on the technology and have a serious accident when a sensor fails (particularly for blind spot detection). I'm still likely going to buy a vehicle with that functionality but am not sure how much I will trust it.