Some people are very very frightened of anything which is not in their science books. Some people are terrified underneath their rationality that maybe, just maybe, something or Someone might exist that they can't measure, probe, put under a microscope or periscope or CAT scan, triturate or grow in a petri dish. How can the mind grasp something that can't be measured by tools invented by human brains?
Often such people like nothing better than to go on "debunking sprees" and belittle anyone, anywhere who does not pay obeisance to whatever science currently tells us is the truth.
I'm not claiming that crop circles are not man made, or that all crop circles (or any of them) are made by guys in space ships. I have no idea, never looked into it, and obviously bunches of them are made by regular humans, maybe all of them.
Just musing about why people love to "debunk" - they're often as intense and agressive about it as Jehovah's Witnesses are with their Awakes and Watchtowers!
(No disrespect meant to any Jehovah's Witness lurkers...)