There's absolutely no substitute for physically looking out of the window with your eyeballs to see what's behind your car. They'll never take away all windows and replace with cams, so why do people insist on not looking out of the rear glass??
Rear view cameras are there as a little extra help incase you can't see the bollard, bin, trolley, bike... CHILD!
Not to mention the obvious, even before you're in the position from where you want to begin reversing, check all your surroundings on approach, then even if you can't see it, you may be conscious of the fact that... "hold on, there were definitely 3 columns there...."
Before the "reverse round a corner" manoeuver on our driving lessons I was told to have a good look into the side street to see what's there first before pulling up and starting to reverse