People have a basic need to wonder why, and how, we are here, on this planet. Religion gives them something that they think might provide the answers. If it wasn't Judaism, and all the others, it would be something else. Those who believe that religion is the answer to 'why are we here' don't care if their religion is based on lies. I think that, since nobody really knows if Genesis is true or not, it doesn't much matter, so long as believers have something, anything, to worship.