Yes, it's completely daft. Even with a hologram 'keeping it all secret', there's virtually no magnetic field on the moon, which means no protection from radiation. Its small mass means virtually no gravity (1/6 of Earth's), and that means no atmosphere - which in turn means no oxygen that 3 billion people would need to breathe. There is no trace of carbon dioxide this huge population would have expired, and no methane produced. And no animals, no plants, no active ecosystem at all that would generate all of the above. Which means no food for 3 billion people to eat. What do they eat, lunar dust?
Occam's razor indeed, as Target says. This idea is almost as absurd as the flat earth.