Why the Need to Fear?

Fear has existed in the world for the beginning of time and still humans cannot eliminate its existence. Certainly fear can be a positive force in certain situations, but generally it can be a very detrimental energy force. It can steer someone in the opposite direction of opportunity or safety. When viewed in a positive light, it can stop a person from doing something that can harm them emotionally, mentally, spiritually or physically. With unhealthy fear comes anxiety, hesitation, resistance to change and progression. So why is it tolerated?