The point is that the known evidence is it is most likely to be humans as it has been shown that CCs are well within the human technology. The sub-point is human imagination is likely to be all that is need to add most of the special effects that give some individuals the idea CCs are non-human in origin.
Just as detectives don't go out and grab the first suspect that happened to cross the site of the crime, but make a case based on motive, opportunity and ... Null! I know there was third criteria*...
Now if the third criteria is particularly good, one may be arrested despite the former two being very weak. But when the third criteria is weak as well as the former two, it goes to the bottom of the hypotheses until the stronger cases are completely ruled out.
While on holidays recently, I saw a tv show on ?AuStar? (an Australian pay-tv network) that showed CC-makers creating CCs. It got down to the last hour and even the CC-makers didn't think they were going to finish it in time. They did.
The show also had scientist in each field explaining why they didn't think the phenomenon particular to their science fields was the result of aliens. I think that there was one scientist still thought the CCs were alien in origin even though that scientist explained why bending of stalks wasn't?
http://www.skepticssa.org.au/html/cropcircles.htmlFunny how the aliens began arriving in significant numbers proportional to human awareness of CCs
The problem with the argument for non-human crop-circles is the strongest case has not been ruled out. The strongest case is that humans are making them, all of them. That doesn't mean we know how humans set up individual cases to look like aliens did it. There are still clever people out there who love a joke.
*Can we stop asking for the third criteria by name and just call it the third criteria?