AGI beliefs don't compare to religious beliefs just because you say so. You simply don't have the same knowledge background as people who think AGI is realistic or even likely. Maybe you have more or better knowledge, or maybe they do... but just saying they're wrong is pointless.

The boundary for systems-level consideration of intelligence is often placed around the brain because that's most convenient, not because nothing interesting happens at larger (sociology, ecology) or smaller (Drosophila, Portia) scales.