On the interstate and in the right lane and some joker passes me and moves over into my lane, the car immediately slows down. If someone is behind me close that is a pretty dangerous situation because the computer is just not letting off the gas but braking in some instances.
The computer in this case is doing EXACTLY what it should do, and what a human should do.
If the guy behind you is following so close, then you are already at risk. If someone cuts in front of you, you are supposed to slow down because you may hit him otherwise and potentially be at fault. Also, the slowing down process - with brakes - is not quite a slam the brakes.
And even in that case, the guy behind you is supposes to be further back and observe someone cutting in. The computer is doing the right thing. Not doing it would mean taking on the risk of rear ending the guy in front of you to avoid the unknown probability of the guy behind you rear ending you instead.
I don't know if the rear brake light are coming on but they should be.
IMHO, in a real world situation you should not really need ACC, you should be paying attention to the road. Some of these fancy features are just giving a distracted driver even more reasons to be distracted. Ok, I will get off my soap box now.
In a logical real world, there would be no cruise control to begin with. It is a dangerous feature. A sleepy driver may naturally ease off the accelerator, minimizing the extent of impact. Cruise control keeps the car at a constant and dangerous speed. It should have been banned long ago.
To the extent that there IS cruise control, is should absolutely be adaptive and designed to slow down the car if there is potential for any impact.