The alternative to ID is of course evolution, which says that the things that exist are not the product of a designer but of chance over time. Given enough time, the theory basically goes, the right conditions will eventually occur and life will begin to exist. There may be fits and starts, but we are theorizing that we have plenty and PLENTY of time, here.
Have you noticed that all of those theories have something in common? The common factor is something eternal. For the person of faith, that thing that is eternal is a deity. For the alien theorist, presumably the aliens either have been around forever, or something created them and something created that. For the evolutionist, maybe the universe has been around forever... although sciency types will generally tell you that the Universe started with a Big Bang, but before that bang there was something that went bang. So that something is, for all intents and purposes, eternal. Or maybe they'd say that time is eternal, or the laws of chance are eternal. But something goes on forever.
Now, if you notice, the longer you think about things like this and the further back you go, the more like the Judeo-Christian God it all starts to look. God is eternal and He is the creator of everything. Now, in some aspects things are different... God is not from another planet (He made them all) and He is not mindless and random. But the more closely you examine just about anything, the more God you will see in it.
I wonder who the aliens think created them?