Arrogantly wrong

The reasoning of the pro-RH crowd, many of them learned people, never fails to astound me.
Why do some people turn against the Truth and yet are so arrogant about it?
In his essay "Heretics", the prince of paradox has this to say:

Nothing more strangely indicates an enormous and silent evil of modern society than the extraordinary use which is made nowadays of the word "orthodox." In former days the heretic was proud of not being a heretic. It was the kingdoms of the world and the police and the judges who were heretics. He was orthodox. He had no pride in having rebelled against them; they had rebelled against him. The armies with their cruel security, the kings with their cold faces, the decorous processes of State, the reasonable processes of law—all these like sheep had gone astray. The man was proud of being orthodox, was proud of being right. If he stood alone in a howling wilderness he was more than a man; he was a church. He was the centre of the universe; it was round him that the stars swung. All the tortures torn out of forgotten hells could not make him admit that he was heretical. But a few modern phrases have made him boast of it. He says, with a conscious laugh, "I suppose I am very heretical," and looks round for applause. The word "heresy" not only means no longer being wrong; it practically means being clear-headed and courageous. The word "orthodoxy" not only no longer means being right; it practically means being wrong. All this can mean one thing, and one thing only. It means that people care less for whether they are philosophically right. For obviously a man ought to confess himself crazy before he confesses himself heretical. The Bohemian, with a red tie, ought to pique himself on his orthodoxy. The dynamiter, laying a bomb, ought to feel that, whatever else he is, at least he is orthodox.
[...]
Suppose that a great commotion arises in the street about something, let us say a lamp-post, which many influential persons desire to pull down. A grey-clad monk, who is the spirit of the Middle Ages, is approached upon the matter, and begins to say, in the arid manner of the Schoolmen, "Let us first of all consider, my brethren, the value of Light. If Light be in itself good--- ". At this point he is somewhat excusably knocked down. All the people make a rush for the lamp-post, the lamp-post is down in ten minutes, and they go about congratulating each other on their unmediaeval practicality. But as things go on they do not work out so easily. Some people have pulled the lamp-post down because they wanted the electric light; some because they wanted old iron; some because they wanted darkness, because their deeds were evil. Some thought it not enough of a lamp-post, some too much; some acted because they wanted to smash municipal machinery; some because they wanted to smash something. And there is war in the night, no man knowing whom he strikes. So, gradually and inevitably, to-day, to-morrow, or the next day, there comes back the conviction that the monk was right after all, and that all depends on what is the philosophy of Light. Only what we might have discussed under the gas-lamp, we now must discuss in the dark.
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