Genesis 1:27: So God created man in his own image, in the image of God he created him; male and female he created them.
That certainly sounds like we should be perfect in body. Unless you want to argue that the Fall rerouted the vagus nerve.
Anyway, you asked why some people might think humans are perfect, and wnoise answered why some people who read the bible might reasonably make that assumption. What exactly is your continued issue here?
Well, I mean they are looking for fact in a thousands year old collection of fairy tales by assorted authors, but they're not particularly any more willingly lazy or stupid...