“Hayek was in many respects a philosophical idealist, in that he believed that ideas rule the world. It was the idea of constructivism, he thought, that has such destructive consequences. If he could combat this idea, then much good would result.”

variant: "I think it would be a good idea" when asked what he thought of Western civilization.
On p. 75 of Ralph Keyes' book The Quote Verifier (2006), Keyes writes: 'During his first visit to England, when asked what he though of modern civilization, Gandhi is said to have told news reporters, "That would be a good idea." The Oxford Dictionary of Quotations cites E. F. Schumacher's Good Work as its source for this Gandhiism, as does Nigel Rees in the Cassell Companion to Quotations. In that 1979 book, Schumacher said he saw Gandhi make this remark in a filmed record of his quizzing by reporters as he disembarked in Southampton while visiting England in 1930. Gandhi did not visit England in 1930. He did attend a roundtable conference on India's future in London the following year. Standard biographies of Gandhi do not report his making any such quip as he disembarked. Most often it has been revised to be Gandhi's assessment of "Western" civilization: "I think it would be a good idea." A retort such as this seems a little flip for Gandhi, and must be regarded as questionable. A comprehensive collection of his observations includes no such remark among twelve entries for "Civilization."'
The quote was attributed to Gandhi in various sources prior to Schumacher's 1979 book mentioned by Keyes above, though none have been found that mention where and when he gave this answer. The earliest located on google books being Reader's Digest, Volume 91 from 1967, p. 52, where it is attributed to a CBS News Special called "The Italians", described here http://www.larchmontgazette.com/news/bernard-birnbaum-cbs-award-winning-producer-dead-at-89/ as "a 1966 look at the nation and its people based on the book by Luigi Barzini", produced by Bernard Birnbaum and one of the 1966/1967 Emmy award winners http://www.infoplease.com/ipa/A0151531.html. A discussion of the quote on "The Quote Investigator" website here http://quoteinvestigator.com/2013/04/23/good-idea/ mentions that on "The Italians" the quote was attributed to Gandhi.
Disputed