Fear is necessary when its function is to protect people from danger. Fear has been evolutionary developed to protect people from death. People are afraid to walk into a forest at night because they are afraid they might be killed by some wild animal. People are afraid of height because they are afraid to fall down and die. These fears make sense, they are necessary, their function is to protect people from death.
There are fears which are also unnecessary. Someone who is afraid of going out in the street on Friday the 13th has an unnecessary fear. There is no danger, no threat, by going into the street on Friday the 13th. Someone who is afraid to cross the street after a black cat crossed it has an unnecessary fear. This fear does not protect someone from death, this fear only is a response to superstition. People who are afraid that aliens will abduct them while they sleep have also an unnecessary fears. There are no aliens, no one ever gets abducted, this fear is completely unnecessary.
The big difference between necessary and unnecessary fear, besides that unnecessary fear is foolish, is that unnecessary fear is like a shadow that is eternally cast over the person. Those who have unnecessary fears constantly have them, they never go away. Necessary fears are not so. When I do normal everyday things I am not worried about being killed by animals, I am not worried about being struck by lightning, I am not worried of heights. When I go to sleep these fears never distress me. Because necessary fears function as an alarm system in people, people become afraid when there is potential danger. Unnecessary fears do not function as an alarm system, they prey on the emotions of people and their stupidities. This is why people who are superstitious always have to worry about which superstition they have violated. Their fear of the superstitious is eternal, never a moment for a peace of mind.
The beautiful thing about skepticism, besides for that we throw away all the false ideas, is that skepticism does not contain any unnecessary fears. I am never afraid that an alien will land in my room as I sleep at night. I am not afraid that some demon or ghost is residing near me. I am not afraid that some curse placed upon me shall come to pass. I have real things to worry about, such as to make sure no person can break in and steal my stuff. But my fears are not eternal. They come and go. For most of the time I have a peaceful mind. There is no eternal shadow cast over me.
Religion is not so. Religion preys on the fears and emotions of people. People are afraid that they will die one day, so religion comforts them by telling them there is a place where they go to when they die. People are afraid that they might be alone, so religion comforts them by telling them there is a God who loves them and wants a relationship with them. Religious people feel comfort from their religion. But they also feel fear from it. Religion makes its practitioners happy as they stay obedient, but they are fearful of the imaginary consequences that will take place if they happen to rebel against it. Religion brings comfort as a substitute for fear, and it instills fear in its members who dare oppose it. Indeed, Judaism teaches to love God but also to fear God.
Religious people have an eternal shadow over them of constant fear. A Jewish teenage boy who tries with all his might to not masturbate will eventually give into the temptation. But once he gives in he will feel this guilt and fear in the action that he is doing. We is afraid that God is watching him masturbate. And he is also afraid that God will judge him for what he is doing at the particular moment. Religious people also carry with them superstitions. If they do something which is not part of their religion then perhaps an evil spirit will haunt them. All of this is an unnecessary fear.
Skepticism can break this fear. It can help free the minds of religious people by allowing them to overcome their eternal fear.