Carbon fiber frames are like anything else. There are good ones and there are bad ones. Granted that metals won't shatter to pieces, but they can still fail in a way that makes you kiss the pavement.
It is in fact possible to make a carbon fiber frame that is way stronger than any alloy frame. Note that jets are made of carbon fiber and planes aren't falling out of the sky. Trouble is most people buying a carbon fiber bike want the lightest weight there is and don't want to pay a fortune for it. And as the saying goes, light, cheap, durable.......pick two.