What a person believes is his own business. If nothing else, that's part of the process of natural selection.
Lives based on a judicious respect for reality tend to be more rewarding.
Those who see clearly and think straight are likelier to reproduce and their offspring are likelier to prosper. Those who choose less rational paths will be replaced, statistically, by those who make better choices, and the human condition will gradually improve. You may think this is cruel, but it identifies a real phenomenon. The idea that wishing will make it so is most deadly when it's applied as public policy. Then, it doesn't matter that you opted to use your head, not when your choices are made for you.