I believe Auto transmission (AT) car drivers are more easily distracted than those driving stick shift or manual transmission (MT)).

But AT makes life easy for so many people, that no one even considers if AT is making drivers less attentive.

A classic example of this, the worst case scenario I have seen in person, is that of a woman talking on a mobile phone in one hand while switching lanes and taking a left turn at a traffic signal. Things like this just wouldn't be possible if that woman was driving a stick shift.

In that driver's case, probably a Tesla like Level 3-5 driving system would be ideal, making it much safer for drivers around.

So, should we go back to MT for everyone or nothing? Just to be under the impression that it's much safer? Or should every vehicle be a level 3 to level 5 autonomous vehicle?

I think people choosing any of the above options will have valid points and research to prove their points. Only time will tell when and how any of those research results continue to hold true.