So I'm actually working on this technology, and every time I see an article about this, there's inevitably some concern about safety, security, government spying, etc.
First off, the reason this technology would be required in all vehicles is that it essentially consists of in-car wifi routers that send their GPS location to other cars. In order for the technology to work properly, all cars would need it, so they can all see each other. Obviously it's a big transition, but it has to be done eventually. New cars would come with the devices built in, and older cars would have after-market devices that can be purchased and installed. However, once in place, vehicle awareness will greatly reduce accidents and increase roadside efficiency. (Think of it this way; The traffic signals are almost always green when you approach an intersection.)
But wouldn't all that be pretty expensive? Not really. The core technology is pretty basic stuff. It's just gps and wifi, really. The fancy stuff, like in-car radar, video cameras, and so forth that you find in some of the luxury cars today isn't really necessary, though from what I gather, it could be plugged in to augment the system. For the most part, consumers won't notice a price change, and in the worst case, they'd have to spend a couple hundred to retrofit their old cars.
All fine and dandy, but what about hackers and people that would abuse the tech? Well, the system is being designed from the ground up to be heavily encrypted and secure. One of the government requirements for the companies developing this is that it meet certain security standards, and since this stuff is used to keep people from dying, you can bet testing will involve trying to exploit every aspect of it. The only issue I can see is malicious signal jamming, though since it requires a unique frequency, people doing this would be caught pretty easily.
Finally, we get to the issue of government spying. Since every vehicle is transmitting its location, doesn't this mean that the government could track everybody, or gather other information about them? This is actually very unlikely. The development of V2V tech has been fairly hands-off on the government's part. Their primary contribution has been to lay down certain standards and requirements for the tech, and then let the commercial companies implement it. One of their requirements has been that none of the data can be used to identify any vehicle in any way, which has certainly been a challenge to implement from the development side.
And to add my own anecdotal evidence, I've looked through all of the code used, from the firmware to the utilities, and I've seen nothing that could be used as a backdoor to get the information. Likewise, I've worked extensively with the hardware and done all kinds of signal analysis, and as far as I can see, there's nothing illicit on the hardware end either.
And don't forget, the V2V tech isn't only being implemented in the US, but Japan, Europe, and China as well. (To the best of my knowledge.) A lot of the hardware and software is shared between the companies working on it and they all have to fit a certain standard.
In any case, I'm sure few people will be placated by my explanation, but I myself would not be averse to having this system installed in my own car.