It is a belief. The Church was caught out as they did not know how to handle the situation. Because many were deceived into thinking evolution was science, it began to permeate our society. Now keep in mind that men are sinful. They are biased against God because they are humanists at heart.
Men love darkness rather than light.
Thus we are more likely to accept that which is wrong than that which is right. You can ascertain that easily enough if you put a Playboy magazine and a Bible on a table, and watch which one people pick up and read. Over the last hundred years, people who were not Christians have readily accepted the evolutionary view, as a belief system which said there was no God, at any rate not the God of the Bible. This means that you are under obligation to no-one. In other words, the belief system of evolution provided a basis for the humanistic morality which said that you could do what you wanted to because nobody owned you-there was and is no right or wrong.