Having said that, this thread is dominated by commenters who refuse to do the math. X-rays sound scary but they aren't death rays; if you add up the numbers you'll see that it's not even worth to talk about them here. There's higher probability they'll harm someone by introducing more cars onto streets.
EDIT: oh, I forgot. The Chart: https://xkcd.com/radiation/.
Bouncing around in the back of a van, something goes wrong. Instead of a rapidly moving beam of x-rays that doesn't stay in one location long enough to cause problems, you get a focused beam.
It many not work that way though. Who knows? That's the problem with being secretive about the whole thing. They don't publicly release data on potential malfunctions.
One of my biggest concerns is the amount of training the operators receive on recognizing and reporting potential malfunctions. I suspect it's not sufficient, but again who knows? They won't talk about it because terrorists.
1. Even if this machine only gives off radiation equivalent to, say, a dental X-ray, I still did not give my consent for it, whereas I did give my consent for the dental X-ray. Consent is important. There are a lot of things that are OK with someone's consent, but not OK otherwise, and we don't have the right to make these decisions for someone. 2. Medical X-rays have positive expected trade-offs for receiving the dose of radiation. Compare this to an X-ray police van than I happen to walk past; there's not really any argument that can be made for why my exposure to this X-ray radiation is worth it for me. 3. The machine can malfunction, or be used improperly, and give off substantially more X-ray radiation than expected or designed. Safeguards are in place for other uses of X-ray to protect against this, e.g. you wear a lead apron to protect the rest of your body during a dental X-ray, and the assistant taking the X-ray leaves the room entirely. Safeguards of these sort aren't possible with the presence of an unknowing public.
There's also of course the entire privacy aspect that we haven't even delved into yet, but the health issues alone are concerning.
You're arguing against a strawman. HN commenters aren't idiots. The technology in question is using ionizing X-rays, which can have harmful health effects.