Reading Neurophilosophy Blog I found this, which I think explains the benefits, nature and place of one of our darkest emotions (or why everything of us is essentially natural, has an role in our practices, and therefore shapes our form of life):
A 44-year-old woman with a rare form of brain damage can literally feel no fear, according to a case study published yesterday in the journal Current Biology. Referred to as SM, she suffers from a genetic condition called Urbach-Wiethe Disease. The condition is extremely rare, with fewer than 300 reported cases since it was first described in 1929, and is caused by a mutation in a gene on chromosome 1, which encodes an extracellular matrix protein. The symptoms vary widely, and in about 50% of cases there is calcification, or hardening, of structures in the medial temporal lobe of the brain. In SM's case, it led to degeneration of the amygdala (below), a small, almond-shaped structure known to be involved in fear and other emotions [...]
SM therefore seems unable to detect threats in her environment and, as a result, does not actively avoid potentially dangerous situations as most of us would. (My emphasis). Feinstein and his colleagues argue that this is because the amygdala is essential in triggering a state of fear. The amygdala is but one component of a network of brain structures that normally generate an appropriate fear response, but in its absence this response cannot be mounted, so that the experience of fear is severely diminished. The researchers further suggest that she may be immune to the effects of post-traumatic stress disorder, and that interventions which target the amygdala could therefore be beneficial for sufferers of the condition.