I don’t believe the circles are created by UFO’s, if UFO’s are understood as spaceships from some other planet. If UFO’s and crop circles are indeed caused by non-human entities, I think they are more akin to occult phenomena than anything else.
UFOs, terrestrial or alien, are an unassailable answer. If you accept the premise of UFOs at the start then it is easy to accept that they construct CCs over night and all the other mysterious aspects of them. The ability to make a CC is kind of minor compared to the flying craft themselves. Especially if it is thought that they come from light years away. Or from another dimension. Or whatever.
It is too easy of an explanation when you start with an unquestioned premise that is far bigger than what you're trying to explain.
I don't know about occult phenomena being responsible. It takes a shaman or group of shamans a great deal of training, dedication and discipline to accomplish relatively minor feats of mind over matter.
Who would commit so much devotion and discipline to make pictures on the ground? To do that wouldn't exactly be a hoax but it would still be a joke. That would be analogous to spending the time, money and technological talent that NASA does on a space shuttle to create a Saturday morning cartoon.