My evidence? The twentieth century.
What bigger and more overwhelming argument could there be than the wars and mass slaughters of the twentieth century.
Yet the experience of the twentieth century has made absolutely no difference at all to the secular Leftist mind-set, perspective and plan; that bland, blind, smug, 'well-intentioned' mechanism of wholesale insatiable destruction.
The Good can be seen as beauty, truth and virtue - leaving aside virtue (which we cannot perceive clearly due to propaganda) is there as single person alive who believes that truthfulness and the creation of beauty are thriving activities in the modern world? That truth and beauty did well throughout the twentieth century? That they did well under secular Leftism?
Yet, just think - the 'modern art'/ modernism movement originated before the twentieth century, and un-rolled unperturbed by everything that happened in the twentieth century; as did advertising, public relations and the mass media. What more could have happened to refute them? Nothing - the refutation, the disaster was as extreme as it is possible to imagine (without utter collapse) yet that made no difference at all.
Because, of course, no amount of experience and knowledge can challenge the assumptions which frame reality. Secular Lefism is 100 percent assumptions.
(No wonder mainstream 20th century philosophy is so hostile to metaphysics; no wonder the mass media is so hostile to metaphysics. When everything depends on your metaphysical assumptions, but these assumption are crudely arbitrary and contrary to common sense, then naturally you don't want to talk about your metaphysical assumptions, or defend them.)
Forget reason, evidence, argument! If wholesale death and enslavement can be ignored/ forgotten, then no argument we might construct will make a difference.
Secular Leftism cannot learn, cannot be taught. If the vast multinational and all-pervading actuality of Communism can fall out of mind, be forgotten, be disregarded; then why wrangle over minutiae.