Fear is a healthy and could be viewed as a “necessary vitamin” for a well balanced human mind. However, fear does and can cause trauma or stress on the individual. If someone suffers from anxiety or other mental conditions that require that stress is to be avoided, consuming fear as part of their diet may be rather difficult, if not an impossibility.
Fear however does not need to be dangerous. It can be and should be experienced through safe media such as horror movies but it also is experienced in other ways. Every day life is enough to inspire fear in an individual. The fear of your boss. The fear of rejection. The fear of change. All of these things and more are examples of fear that may but smaller or larger depending on the individual but these are examples of fear that should still be dealt with regardless.
If someone is prescribed to avoid stress; that person is being sentenced to avoid what life offers. It is good to experience fear regularly so that individuals know how to handle it when the time comes. Consuming fear through horror is something that can, among other amazing things (such as raise your immune system), act as a mental exercise and can lead to a better quality of life. Perhaps the horror medium is some sort of gateway to people who can’t handle the stress of life, to start building up to it by handling fictional challenges. Maybe its exactly what they need.