If an MRI scan is truly practically harmless, and its only consequence is the information you get from it, then it's not the MRI who is causing the harm, but our own response to it

"Avoiding MRI scans" as a solution is a hack, you are trapped in a local minima solving the problem very indirectly. I may be willing to accept it as a temporarily pragmatic solution because solving our medical system may be very hard and bureaucratic

But, according to your arguments, the real problem then would be how we react to the results of a scan. Whether it is how patients react to them, or how the medical system reacts.

If full-body scan only informs, then do not kill the messenger!