First among the reasons for this large-scale architectural vandalism was the prolonged revulsion against all things Victorian. In Britain this was particularly pronounced after the war because for the first time it was unmistakably clear just how far the country had declined from its Victorian apogee of world power and influence: a decline made somewhat easier to bear, psychologically speaking, by the consistent, unabashed denigration not only of the Victorians themselves but of all their ideas and works as well.This is an echo of the war against traditional morality, one that might achieve greater venom as the hip and modern crowd compares the world they've created - massive debt, higher child abuse, babies stabbed in their spines by abortionists, sex slavery supported by Planned Parenthood, rampant addiction to porn, etc. - to the one of our prudish ancestors.
I witnessed a striking example of this revulsion in my own household, My father, a communist and therefore predisposed to view the past in a lurid light, especially by comparison with the inevitable post-revolutionary glories to come, had bought several Victorian paintings at Sotheby's during the war for ten shillings each. (Communists are not necessarily opposed to taking advantage of a temporary depression in prices.) He kept them in the loft of the house. Then, one day in 1960, quite arbitrarily, he decided that they were taking up too much space—unlike the tins of fruit he had stockpiled during the Korean War in the expectation that it would escalate into the Third World War, and which were now beginning to explode, but which he kept forever. He took all the paintings except one and put them on a bonfire, an act which I knew even at the age of ten to be one of terrible barbarism. I begged him not to do it to give the paintings away if he didn't like them—but no, they had to be destroyed.
It's easier to hate the past than to admit you made a mistake.