1. Car makers can put whatever devices in their cars they want. It's up to you, the buyer, to either not buy cars with black boxes OR to petition your local/state/federal politicians to make selling cars with black boxes illegal. You have either choice, it's up to you.
I have done both. I made sure that the car I bought did not have a black box and I have written to my politicians for the past several years. Every single politician replied with their standard form letter, indicating that no one read shit in my letter. I've even called and left messages or spoke with someone in the office, but never the politician themselves. They all spew forth the safety issues and that I should just go along with it because they're looking out for my safety and everyone's best interests.
The fact that the black boxes may now be required means that I won't have a choice and, as usual, politicians could give a fuck.
2. Insurance companies can require black boxes in cars if they were factory installed in order to be insured. Though there may be laws that they might be breaking because many states require auto insurance, but I'm not a lawyer. Either way, again, two options: vote with your wallet or make this practice illegal by approaching your politicians.
Some insurance companies, such as Progressive, already have little devices that you can attach to your car to record certain things. They promote it as a way to monitor your teen driver and they give anyone who uses it a discount. Sure, it's a discount now, but you know that, eventually, it's going to be a requirement. That's how it works. In some states where black boxes would be questionable legally, they will just offer a discount to have access to that data and, when all insurance companies in the state do this, you are essentially paying more for your privacy.
The politicians, again, don't really care about this. You have a few that pay attention and make a big stink, which is why it hasn't happened yet, but the National Highway Traffic Safety Administration, apparently, can make this a requirement and there's little we can do about it because so few politicians actually care.
3. The aforementioned black box information does not have to be admissible in court for criminal penalties, but insurance companies could black ball you for information obtained from the box. Also, affected victims do have the 100% right to go after you for CIVIL penalties related to any crashes. The only time the 'government' matters is when there is involvement of criminal penalty. A civil court could mandate that the black box information be passed over to the victimized parties for review, or the data retrieved from therein.
If insurance companies can blackball you, then they could do that at any time, for any reason and you would have very little control over their decisions why. What if you consistently drive 79 in a 75 and the insurance company doesn't like that. You're tossed off the insurance. Sure, that's technically speeding, but everyone does it. What happens when you always stop 1.5 seconds at a stop sign and not the 2 seconds dictated by law? Your insurance can drop you then, too. How about you take corners too hard, you break too heavily, or don't put your headlights on at the right time? You might think these are a stretch, but when it comes to money, insurance companies are quite petty and like their profits. They might not blackball you, but they'll find a way to charge you more for insurance.
As an example, I was pulled over by the police a few months back. I was at a red light. The left arrow turned green, so I went. The police, who was two cars behind me at the red light, pulled me over. My crime? The cop said I pulled away from the light too quickly and he thought I should have done it slower. I got a warning. Now, under this system, where the insurance company has this data, they can question why I stopped, started, then stopped again. They can already pull my DMV record. Well, now they could decide the cop was right and raise my rates.
You're damned right this is a privacy issue. If I have done something wrong, then let the courts petition for my private information. It shouldn't be readily available to anyone, be it police, insurance company, or private individual. If the government needs a warrant for my private information, then they should as well. Your phone records used to be available only by court order. That's not totally true now. Then again, it's for our own safety right? Only bad guys would want to keep any of this information private.