The problem is that whilst the writer has studied psych and economics he has not studied politics.
So essentially he is a trained pyschologist attempting to use his knowledge to justify his personal feelings and biases. In allegorical terms he is attempting to define a walnut without knowing anything about its shell. He is only accredited in half of what he is writing about.
Even the short excerpt clearly shows this as he overlooks basic definitions used to discribe poltics. There are four categories into which anyone can fall; radical, progressive, conservative and regressive. They are broadly speaking; believe that society must be torn down and built anew, believe that society is fundamentally good but needs some reforms, believe that everything is just about right, believe that society has gone to far and must return to old practices. In short radicals support drastic change, progressives support some change, conservatives resist all change and reactionaries want to roll back previous changes.
Various political ideologies can fit anywhere in this spectrum and indeed they naturally shift with time. For example when communism first appeared in Russia it was a radical philosophy and (for a brief period) co-existed with moderate elements. When they reached power they radically chnaged society, however having done so they then resisted all chnage becoming conservative. Now as communism in Russia has fallen communists in Russia (especially old ones) are reactionary.
Ideologies cut across society vertically and are constants however radical/progressive/conservative/reactionary definitions cut across society horizontally and are not constant they are defined by the society in which they exist (as such varying with both time and space).
In this way communism can be radical, progressive, conserative and reactionary all at the same time but in different places eg communism is now radical in the US, progressive(yes stretching the term abit) in socialist states (eg sweden again a slight stretch), conservative in China and reactionary in Russia. People and movements are united across borders not by their status in society r/p/c/r but by the ideology they espouse.
So basically the author is trying to deniggerate left-wing (by which he actually means social-libetarians) by writing a critique of the psychological makeup of progressives.