A human with one eye can't see three dimensionally, thus would have depth perception problems. For or a step can't be seen as a 3D object that ‘stands out’. Instead the 3d image is reduced to 2D, which flattens the object to where the single eye sees the surface but not the depth, resulting in many falls,etc. (I know from personal experience) The full scope of vision is cut in half.
If, say, we had one eye in the middle of the forehead, we would still have to deal with peripheral vision to deal with or maybe not….If humans were predominantly born with one eye perhaps it would be a normal thing..