At first I thought, if I were Superman, a perfect secret identity would be "Clark Kent, Dentist," because you could save money on tooth X-rays. But then I thought, if a patient said, "How's my back tooth?" and you just looked at it with your X-ray vision and said, "Oh it's okay," then the patient would probably say, "Aren't you going to take an X-ray, stupid?" and you'd say, "Aw **** you, get outta here," and then he probably wouldn't even pay his bill.
Fear can sometimes be a useful emotion. For instance, let's say you're an astronaught on the moon and you fear that your partner has been turned into Dracula. The next time he goes out for the moon pieces, wham!, you just slam the door behind him and blast off. He might call you on the radio and say he's not Dracula, but you just say, "Think again, bat man."