Yes ... there are many instances when we know something to be real, but do not act accordingly.
But it could be irrational. If people were governed by reason, we'd be a lot closer to utopia.
I think there are significant distinctions. You can't put 'God', 'Bigfoot', 'Unicorns' in the same category, and thereby argue that if you don't believe in one, it's the same reason for the others.
Here's one for you:
I don't believe in numbers. Numbers don't exist, they're entirely a construct in the mind. I do, however, have absolute faith in mathematics. Pythagoras' Theorem is always true.
So numbers are a construct which, so far, have carried us to the limits of the cosmos, and so far, I think, have never let us down.
But you can't show me a number.
The first step is accepting that our 'accepting an unreality' is flawed.
The next step is asking why I should accept my understanding is flawed.
At this point, you begin to see the difference between arguing for or against the existence of Bigfoot, and arguing for or against the existence of God.