It prevents the truth from being perceived.

It enables charlatans to find dupes, and causes the real magician to be applauded as a legerdemainist.

This is what the New Testament tells us happened in the case of Jesus Christ.

His miracles failed to convince because the people had for a long time loved those who could deceive them cleverly.[1] The people said to him, "Thou hast a devil," and others warned them after his death saying, "That deceiver said while he was yet alive 'After three days I will rise again.'" When people are taught not only to marvel at the marvelous but to be indifferent to its falsehoods they lose the power of discrimination, and are apt to take the true for the false, the real for the unreal.
For an evening's healthy enjoyment I believe a circus is as good a place as can be found anywhere.

The air there is not close and vitiated as in a theater; you can spend two or three hours comfortably without inhaling noxious atmospheres.