Why do we need a purpose to be alive here on Earth? Just be happy and live your life to the fullest and be good to other humans and animals.

Great rap! Love the Richard Feynman sampling. Like Greydon Square, I now make my own purpose ... but I didn't used to. As a Christian, I once believed that God had a plan, and that our purpose was to glorify him. But when I began to doubt I thought, what a crappy planner God was, and wondered, what kind of supreme being would demand the worship and adoration of his tiny little subjects? I find Dan Barker's response to the question spot on:

“Asking, "If there is no God, what is the purpose of life?" is like asking, "If there is no master, whose slave will I be?" If your purpose of life is to submit as a slave, then your meaning comes from flattering the ego of a person whom you should detest.”

Why do we need some all encompassing great purpose?
My Raison d'être is my family and to hopefully make their lives happier than mine was, I chose that "purpose" If I succeed or fail I am only answerable to me and only then until I peg out.

I say we have no purpose.An earth worm has more of a purpose in regards to the betterment of this planet than a animal that pollutes destroys and eradicates any thing that gets in the way of profit.