The problem is that x-rays use ionizing radiation which is more dangerous. Some people could be more sensitive or in a more likely scenario they get a lot of x-rays and/or ct scans due to medical issues which requires them being very careful about spacing out scans and exposure to other sources.

Then there is the possibility someone walks in between the van and target. At some point you have to stop the argument that this and that does x and y so z is ok. People are afraid of excessive radiation and the government isn't listening to people.

One thing that infuriates me is that people making these arguments don't even know that x-rays (and cats) use ionizing radiation which is what carries real risks. Incidentally, MRIs do not use ionizing radiation so you can stay in there a "while". Thats how they can do so many cool studies using MRIs.