And in fairness to the TSA and the manufacturers of the scanning hardware, that page shows as last being updated 12 years ago ("Updated April 8, 2003"). Scanning technology has improved markedly since then, according to what I've read.
But it would still follow the same common sense logic...
No matter how bad it is, less (12 years later) is always going to be better than more (12 years earlier), when one can't judge the absolute degree of danger for any given sample of film.
Ken