As with many online debates, this one seems to be based on a difference in definitions. Some people take "self-driving cars" to mean "cars without a steering wheel that will drive my drunk butt around in the rain", or even "no more human cars on the road". I still honestly think that this will never happen without radical changes to our roads, cities, laws, and economy. Others view "self-driving cars" as an extension of cruise control that might eventually become fully automated. This can be already be seen in cars by Tesla, etc.

I think the "5+ years before it's viable" crowd is mostly responding to drum-beaters of the former, not the latter.