Cruise control is a killer. It totally kills your reaction time, many times resulting the death of those that use it.
I think that depends on the driver and how they use it.
Whether I'm using cruise control or not, if my right foot isn't on the gas pedal then it's covering the brake pedal, ready to press it.
If you're trying to say that the amount a vehicle slows between taking your foot off the gas when not using cruise control and putting it on the brake pedal is enough to prevent an accident, I have to say that the only cases where that would be true are:
1)The driver wasn't paying any attention.
2)Their reaction time sucked anyway, cruise control simply made it result in an accident more sooner than later.