Well, if you agree humans cannot be ideal rational thinkers, then whats the point of bringing it up? We gain nothing with it.
Humans cannot be ideal anything. We cant be ideal parents or ideal employees. We cannot be ideal athletes or ideal mathematicians.
We may not be able to achieve perfection but we can approximate it to the best of our ability. Yes we are guaranteed to fall short but to the degree we succeed everyone benefits.
But you dont know how wrong you are if you dont know the real truth, therefore you could be 99% wrong about god and you wouldnt know it.