Actually, the last statement (about spankings instead of jails) doesn't sound foolish at all. We abolished torture and slavery, we have replaced a lot of punishments with softer ones, we are trying to make executions painless and more and more people are against death penalty, we are more and more concerned about the well-being of ever larger groups (white men, then women, then other "races", then children), we pay attention to personal freedom, we think inmates are entitled to human rights, and if we care more about preventing further misdeeds than punishing the culprit, jails may not be efficient. I doubt spanking will replace jail, but I'd bet on something along these lines.
I think that the idea of spanking replacing jail is very unlikely, but doesn't sound as absurd as most of them on the list.
The thing that makes it sound absurd is the idea that our grandchildren will find it EVIL to put criminals in jail instead of spanking them. Imagine people 100 years from now pointing to revered historical figures and saying they supported the use of jails, the way people point out that some of America's Founding Fathers owned slaves.
Although... if you accept the premise of other punishments replacing jail, I wouldn't be entirely surpr...
Suppose I told you that I knew for a fact that the following statements were true:
You’d think I was crazy, right?
Now suppose it were the year 1901, and you had to choose between believing those statements I have just offered, and believing statements like the following:
Based on a comment of Robin Hanson’s: “I wonder if one could describe in enough detail a fictional story of an alternative reality, a reality that our ancestors could not distinguish from the truth, in order to make it very clear how surprising the truth turned out to be.”1
1Source: http://lesswrong.com/lw/j0/making_history_available/ewg.