It's part of the insidious effect of the denialist mindset that the believers must have something wrong with them. That they are stupid, or crazy, or fanatics of some fantastical worldview. So complete is their denial of the evidence that they project all their boogeymen on others and reinforce for themselves that they are the sole possessors of the truth. It's really a religious attitude that worships science and critical thinking as the only way of knowing the truth. Hence it quickly degenerates into a moral issue--practice our "critical thinking" or else be condemned as a fool or idiot or even be banned.