Even when it doesn't slam on the brakes, if you were concentrating on the road, those jarring beeps can just as easily break your focus on driving as they can break your focus on a distraction. I think it's better to avoid distraction by keeping cruise control off, and you can compensate for having human-level reaction time by following at a safe distance and staying in an appropriate gear or setting an appropriate level of regenerative braking to avoid mindlessly getting too close to the car in front of you.
I think that too often, driver assist features are being added to cars to compensate for the other features (like adaptive cruise control) that encourage drivers to mentally disengage from the task of driving. There's also the fact (well, opinion) that driving a car without electronic assists and nannies is fun and engaging (especially on back roads with the windows down and the radio up). Riding in an autonomous vehicle is just as dull as riding on public transportation, all while being less efficient, less social, and worse for the environment.
It would be interesting if we could somehow test how the reduction in crashes with the introduction of driver assists would compare with if we had just banned cruise control, introduced minimum visibility and minimum suspension stiffness standards, and mandated manual transmissions.