You may have observed that you get the best fit to activist behavior if you assign a value of 4.0 to the emotional age of activists. The evolution of liberal activist attitudes described by Siegel can be entirely explained by the "Well I never really wanted that anyway!" response.[I edited out a redundant "either".]
As Siegel notes, everything promised by the Left was being achieved, even over-achieved, by 1960. The problem was, it was being achieved without the Left's methods. We were coming off 8 years of Eisenhower and gray flannel suits, remember? So the Left [...] had to either admit that 1950s free enterprise and gray flannelism worked at least as well as Leftism, or declare "Well I never really wanted that anyway!"
They chose the latter course. Not for the last time either.
To make a long story short, 80 years ago, socialism was a moral imperative because it was the best way to create smoke-belching factories and deliver copious goods to the masses. 40 years ago, socialism was a moral imperative because it was the best way to prevent smoke-belching factories while still delivering copious goods to the masses. The Wall fell, and today socialism is a moral imperative because it's the best way to prevent smoke-belching factories and keep copious goods out of the piggish hands of the masses.
From the environmentalist revolution of the 1960s until after the collapse of Soviet Communism, it was axiomatic on the Left that socialist governments would be incomparably better stewards of the environment than capitalist governments. But once the socialist governments fell, it became undeniable that they had, in fact, been worse. There needed to be some way that capitalism was still wrong. Since capitalism had long ago proven to be more productive, and since it was now undeniable that the productivity had not been bought with greater environmental impact, there was only one path left. Productivity had to be a bad thing. Sure, at one time socialism had been supposedly superior because it was supposedly more productive. But that was then. This is now.
And so, we have locavores. Capitalism is able to bring you strawberries in February? BAD! BAD! BAD CAPITALISM!