Kandinsky
Curious Cat
Just to clarify. I think Complex Crop Circles are made by human beings because the people making them are telling us that they are and the evidence of human manufacture is there to see if you know what to look for.
Excellent post.
It's worth adding that CCCs are also regionally and culturally specific too. Including all the points you've raised, believers in paranormal/alien CCs need to explain why aliens are focused on places like Wiltshire, England. Whilst they're at it, they could explain the general rise in complexity since the mid-80s. Art-forms tend to grow in sophistication over time...just like the CCs.
These all point to human origin.