Why would the world be better off without religion?

I see this claim every so often. How and why would the world be better off without religion?

Would there be nothing else humans would fight over or become radicalized by? Would people suddenly somehow think perfectly logically? Would there be no more "us vs. them" thinking or no more self-righteous and hypothetical leadership?

What terrible things have humans done that are specifically and exclusively the fault of religion?

Why would the world be better off without religion?
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