Nobody is going to disagree that windows should give as much visibility as possible and people should know how to drive with them, but it's not physically possible to see something (or someone) on the ground close behind your car without a camera. I'd recommend testing with a traffic cone or something, I think you might be surprised how far back a little kid has to be before you can see them in the mirror even in a small car.

If you won't use them, you should at least be happy that other people have them so they don't back into you. Cars are dangerous.

https://www.consumerreports.org/cro/2012/03/the-danger-of-bl...

https://www.iihs.org/news/detail/rearview-cameras-reduce-pol...