It's the absence of belief in a deity - and therefore the recognition that the starting conditions of our lives was random chance, out of our control - that provides the foundation that all humans are equal and of equal value. That after 14 billion years of my atoms circling the universe I sprung forth, child of middle-class but reasonably well-educated parents in the United States, and not the child of struggling farmers in Australia, or drug addicts in Eastern Europe, was complete chance. To me this means that I am of no more importance than people born to those situations, irrespective of what they eventually managed to accomplish.
It's the absence of belief in a deity - and therefore the realization that life is finite, precious, non-transferable, and fair in so far as much is the product of chance - that means we should prefer human life over sentient robots. The consciousness of a one-day sentient robot will likely be transferrable, and therefore durable mostly indefinitely. Mine consciousness is, as of yet, not.
It's the absence of belief in a deity that neatly solves the problem of evil in the world. And so on, and so forth.
I'm happy for people to be comforted by religion, as they hurtle through a probabilistic universe, trying to fill the time between their birth and their death with meaning and enjoyment. When we die, it's unlikely that even a single lifetime later people then alive will even know or think about how we ever existed. So do what you must to be comfortable now. It'll all be over soon.