This assumes a single machine scanning, not a botnet of 1000 or even the 1.5m the dutch gov't collected 2 yrs ago. Again, a sane discussion is in order. Scanning isn't AS EASY, but it certainly is still feasible, With 1.5 million hosts it will only take 3500 years... for a _single_ /64!
I'm not sure that's what I would call feasible.
I would call that not understanding today's security world. "Scanning" is not the primary mode of looking for vulnerabilities today. There are several more effective "come here and get infected" and "click on this attachment and get infected" techniques. What scanning that does go on today usually not the "lets scan the Internet." No money in it. You target your scans to the address ranges of the sites you are trying to mine (i.e. build BOTNETs) or go after.