It's not like that at all. It's like understanding the physics behind a vast, totally random dust cloud that appears to be 99.9999999999999999999999999999999% hostile to terrestrial life and presuming initially that there is no designer. It would be like that.
There is nothing to prevent a rational adult from nonetheless concluding Christianity from his observations of the cosmos, even from noting the apparent random nature of the observable universe. It would, however, be silly/absurd to deny this appearance, and instead describe it as "optimized" and/or "finely tuned" for terrestrial life. The apparent random nature of the observable universe has been sufficient for some/many to require something more to be convinced of a "designer."
It would be entirely reasonable for a Christian to wonder if God is merely the deity of this one infinitesimal speck called "Earth," and to wonder why there aren't more nearby planets teeming with more of God's life. Is God the deity of vast nothingness devoid of life? Couldn't He have put about 40,000 Dyson spheres within close proximity of each other, with each one being equivalent to a few million earths, each with vast resources to support His children, without them having to go to war all the time, fighting over scarce resources? Of course, this is just one question that comes to mind, and it shows why God isn't necessarily presumed.
Again, there's nothing that discounts Christianity either. It's just not the case that the observable universe is itself any sort of proof.
