It is definitely an advantage for humans to possess the reflex that is the fight or flight response. As a psychiatrist, I mainly see the detrimental and negative consequences of the fight or flight response gone awry in response to anxiety. But the fight or flight response is definitely an advantage for survival, and without it, you would be less able to save yourself from real dangers in the environment.
So let’s go back to one of the beginning scenes of the movie Ghost, where Sam Wheat (Patrick Swayze) and Molly (Demi Moore) are walking down a dark street after a night out at the theatre. Then a mugger shows up, holding the couple up at gunpoint. What occurs to Sam’s body? Well, he sees the mugger and the gun, so this sets up a cascade of events in his body known as the fight or flight response. With the danger of the gunpoint mugging, Sam perceives the imminent danger and sends a neuronal signal from his amygdala, a part of the brain that senses danger, to the hypothalamus and pituitary gland (another part of the brain), which then sends a hormonal signal to the adrenal glands (sits on top of the kidneys), which then releases adrenaline. The adrenaline helps Sam’s body to prepare to fight, or to run from the danger. This is an instantaneous response that only takes a few seconds. The adrenaline increases the heart rate and increases the breathing rate to carry more oxygen to the skeletal muscles, in preparation for fighting or running. There is also a shunting, or redirection, of blood from non-essential organs (such as the skin and reproductive system) to the skeletal muscles. Sam’s muscles also tense up in preparation for the fight or flight, and his vision and alertness sharpens to deal with the danger. In the movie, Sam elects to fight, but he ends up being shot and dying. Nonetheless, although Sam ends up dying, his chances for survival were increased with his fight or flight response- this response only took a few seconds without Sam even thinking about it. Imagine if Sam did not have this fight or flight response, which is really a reflex. Sam would sense the danger, and then he would have to spend precious time trying to figure out whether or not this was a danger. Then he would have to think about his next options to deal with the threat, and this could take minutes. Still, even if he were still alive to carry out his options, he would need to take time to prepare, like consciously breathing deeper and progressively tensing his muscles at will. This process of actively trying to think of how to deal with the danger will kill you off in the process of taking the time to actively think about how to deal with the danger. With the fight or flight response, no thinking is involved…it is automatic and instantaneous, giving Sam the best chance for survival.