Most of us do. But people who only have sight in one eye have no difficulty perceiving three dimensions. And some fairly large percentage of people with binocular vision are stereoblind, typically without even realizing it.
If anything, I'd say it's not that
> We're aided in converting our 2x 2D sight into 3D mental models through the use of color and parallax.
so much as that we're aided in converting our 2D sight into 3D mental models through the use of stuff like color and parallax through the use of stereopsis.