I understand your skepticism 100%, but I suspect you might change your mind if you, say, rented a car with it for a week. It's definitely a net positive for safety, and it probably costs the auto maker less than the seat belts (literally).
ive owned two cars. the modern backup camera means the new one has small "stylish...." rear windows. it is wayyyy more dangerous than the older one with no sensors
i only have those two data points; but give me an older car with larger windows every. single. time.
I've owned cars with backup cameras since about 2014. I still mostly back up the old fashioned way, and really only use the camera for very tight situations where a few inches matter.