Why? What is our responsibility to self and others?

"Like Angels on earth." - No we're not! That title goes to dogs and cats. 😅

We are stewards, as you say. Our principal responsibility is to leave our universal inheritance in a good condition so that it can be used by future generations.

More people adopting a less self-centered mindset would make such a difference.

More likely, God is a human construct invented to explain how everything came about.

The simplest most rational explanation always makes the most sense.