i see this as something that will reduce your insurance policy. they can track your statistics and if you fall within the 'I follow the rules' category your premium should be reduced accordingly. if you are a wreckless driver well then you should pay the penalty.
besides the above, as a woman who drives a lot on my own and at night because of shift work and at those times there is not a big police presence I would appreciate the safety issue of a black box in the event of a hijack or some other security issue.
privacy is a concern but one can rather go to a motel (if this is the privacy concern) than use your car.