Don't knock adaptive cruise control until you try it. It is significantly better than plain-vanilla cruise control. I've found that when I use it, I tend to stop caring about if I'm driving "too slow" -- it makes me a less aggressive driver.
My current car has it. The person you're replying to is still correct, if you need to "disengage from driving" then pull over and take a break.
Adaptive cruise control makes driving less stressful/more pleasant but you still have to be mentally there. No system is full proof, and certainly not at this stage.
