Why do we believe or disbelieve 'GOD'??

Since my  childhood I observed believing or disbelieving of a supreme being is imposed by the society . No one has ever bothered to know the fact/truth .Since my childhood i have not seen a person neither believe nor disbelieve in god. I have never heard a statement that neither believing nor disbelieving doesn't matters . 

Why is there so fear deep down in our heart regarding to the presence of  GOD?How can we know the actual truth ?Why are we so god feared? Why is always a fear required to do some thing ?i.e if we do or don't do this it is a sin etc.. Why this authority has been preimposed in the society?

Doing the action for its sake not for that something would happen or someone would think of bad about me if not done in the manner they have taught.This has to be the best lesson one can learn from the life and a think a little bit of curiosity takes us to the state of mind .The mind that Rabindranath tagore talked in his geetanjali that goes as below...

Where the mind is without fear and the head is held high;

Where knowledge is free;

Where the world has not been broken up into fragments by narrow domestic walls;

Where words come out from the depth of truth;

Where tireless striving stretches its arms towards perfection;

Where the clear stream of reason has not lost its way into the dreary desert 

sand of dead habit;

Where the mind is led forward by thee into ever-widening thought and action–

Into that heaven of freedom, my Father, let my country awake.

Is the authority important to know what is to be done and what not to be done?