Your characterization of autopilot as “just cruise control” is fundamentally incorrect. Mere cruise control still demands significant and continuous attention and manual control on your behalf (steering). Autosteer makes the leap to fully automatic, which opens the door to not paying attention for long stretches of time.
From a practical perspective, Autopilot still needs to be monitored. But more relevant to this discussion, the user still needs to interact with the car to keep Autopilot engaged. It is possible to do that while paying very little attention. It is also possible to drive a car with cruise control while paying very little attention. Both systems can be abused. I have already said Tesla should do a better job of trying to crack down on the abuse of Autopilot. But I don't know why it is controversial to say that if used properly both systems can lead to greater safety by allowing the driver to focus on other aspects of driving.
You're just trying to make them sound similar, e.g. "if used properly" or "both can be abused". But there is an ocean of difference. It is vastly easier to ignore a system that is capable of driverless operation for long periods of time.
But it isn't fully assisted and doesn't completely remove the need for interaction. It just is another step forward from cruise control that is more assisted and requires less interaction. I am not sure why everyone assumes the sweet spot for driver assistance ends immediately after adaptive cruise control and before cruise control plus lane keeping.
>Your brain will stop spending power on backseat driving
That is an interesting phrase to use considering backseat drivers have zero responsibility or control of a car but still manage to pay attention.