The Before Time Book

Maybe this was asked before but why are they so afraid about people seeing the Georgia book from the before times ? Surely they must know that the world wasn’t always a barren wasteland? I can understand why they’d want to collect a relic but how would knowing that the earth was once beautiful cause a meltdown in society. The “famous” silo saying already says “we do not know when it will be safe” and by looking outside they can see it doesn’t look like the book. Thanks