We want people to be ethical, right? To teach people morals you need to speak with authority. If you tell people patent nonsense you undermine your authority and you undermine the morality of our culture. Primitive people could not prove that the story of Noah and the Earth flooding was a complete lie, we can.
The greatest lesson that these primitive religions teach the children of society today is that hypocrisy is acceptable. You can lie through your teeth and be a teacher of morals.
The Christian bible, and all the others I know about, pretend to be absolute truth and yet they are filled with lies and what other conclusion can children draw except that lying is acceptable, and that all adults are hypocrites?
This is a disease that society has. Religion is a social disease.