'The ultimate authority must always rest with the individual’s own reason and critical analysis.' -Dalai Lama.
Believing in something that you have not understood/experienced is lying to oneself. Blind believer convinces himself that what he believes in is true, even if he has no solid logic to support it. So, blind belief is a lie that you tell yourself. And then, you tell that to your children and train them to lie to themselves and pass it on. It rids you of your inherent curiosity and the ability to think for yourself. Religious people often warn and say: 'Do not doubt!'. This is true for all religions. Almost every religion today has some philosophy and some blind belief in it. These two terms are contradictory and thus one must win. As the conscious are outnumbered hugely by the unconscious, almost always, blind belief wins.
The founder starts off the religion with some philosophy. After he dies, his unconscious successors are bound to corrupt the religion with blind belief. If the founder can light up the spark in his successors, and they in-turn can light up the spark in their successors, only then the religion can remain alive.
Once the chain of enlightened successors is broken, the unconsciousness of the unconscious successor(s) reflects in their words, and gets inside the religion. Or, if the unconsciousness gets inside from the unconsciousness of the followers, it can go unchecked and grow until it's too late. Blind belief is one popular and obvious consequence of that unconsciousness. Such a religion will push people further in their dreams instead of waking them up. Or, it will take away their worldly dreams and give them better ones which will make them even more unconscious.
Once blind belief enters the religion, it cannot be removed. That process is non reversible. If one conscious person tries to show the truth about those beliefs, he will get discarded. Those beliefs will become part of that religion forever. The conscious will then have to start a new branch of the religion or will have to start a new religion altogether.
Once you give up the need of reason or validation, it will affect you in all areas of life. You cannot keep on doubting everything else and not doubt your religious blind beliefs. Either you will start doubting your blind beliefs or you will eventually stop doubting everything.