The word from a silent sky

Yesterday I read Karl Schroeder's post on a new paper on the Fermi Paradox. Karl makes the interesting suggestion that if aliens exist, their technologies are indistinguishable from natural objects. Karl had come up with the idea of a technology indistinguishable from nature in the quite different context of trying to imagine the future development of our technology. He takes the apparent absence of aliens as at least consistent with this projection: if it holds true for us, and if we are not alone, and if we are a typical intelligent species, then a Galaxy swarming with alien civilizations would look (to us, now) just like a Galaxy with no aliens at all. So what we see (and, more to the point, don't see) is just what we would expect.

It strikes me that the arguments over the existence of aliens have an interesting structural similarity to certain arguments over the existence of God. There's a type of atheist argument that says, in so many words, that the non-existence of God is manifest by just looking out of the window: if God existed, we would know about it. There's a type of theist argument that says if God exists, his existence is necessarily hidden from us, and the world outside the window - a universe that looks as if it works all by itself - is just what we would expect.

Discuss.