What is fear?
It is the evolutionary response built into our brain when we are about to do something new or we are in a new situation. It makes you evaluate carefully the pros and cons of doing something, carefully scan your environment to understand if there are anythings which could be life threatening.
This was at least the evolutionary origin of this feeling. When men was resting in a cave at night, "fear" of getting eaten by carnivorous animals would prevent him from getting out of the cave and risking himself.
But as society evolved, and got more safer - at least from a danger to our life perspective, this feeling didn't just go away. Many situations where we now feel fear, our life is not at stake - but we still feel it. It may be fear of doing something new, something which we have not done before. It doesn't necessarily kill us - but may hamper our chances in life. It may be triggered by the anticipation of facing rejection from the girl you love. Or from loss in social esteem in front of your colleagues or friends.
And if you consider groups of people as units, fear takes a new turn of its own. Societies can start fearing punishment by govt. Or what we are facing now, a deadly virus. The whole human civilization is fearing it ( though in this case, it is actually case of life and death).
But apart from situation like now, when there is real danger of losing life, I think "fear" situation more than we need it. There are many experiments which prove that humans are loss averse. We fear a new situation more than we should. We are more happy in status quo.
Why are we so? May be the way evolution has chosen our genes, those early humans who played more conservatively were able to survive more and hence pass their gene. People who were more adventurous - died early.