The argument I've seen made for crating from an evolutionary-history perspective is that dogs are den animals -- they actively like having a small nook that they can feel safe in, where they're comfortable and nothing can sneak up on them.

I have a crate for my dog. The door stays open all the time, it has a comfy mat on its floor, and sometimes he goes there to take a nap. He's only ever shut in it when there's a reason -- a contractor in the house, or I need to keep the front door propped open for a while, or similar. (When he was a puppy it was incredibly useful, though, because it was a way to teach him to settle down.)