All your assertions are undoubtedly correct as I believe that the case has now been proven, but the practical problems of persuading security (certainly in the UK and some other countries, and maybe moreso in the US too recently?) to hand check film mean that my film ends up going through the x-ray machine on the majority of occasions whether I like it or not. Being honest, in a lot of cases I've given up having the argument as (a) if I loose it often ends up that the ramp up the x-ray just to get me back and (b) I'm one of those people who'd claim no NOTICABLE effect from having film x-rayed somewhat more than once or twice. Of course, slower film helps here, as it is less affected by x-rays than faster film (hurrah for K64
Pragmatically, I believe that the best we can hope to do these days is reduce to a minimum the number of times a film passes through a machine, and if x-rayed film is brought back from a trip its probably best not to take it on the next trip but to use it at home. One thing I wouldn't particularly recommend is one of those x-ray bags - as soon as the security guys see the black blob of the shielded bag on their screen, they ramp up the power to see through it, negating the benefit of the bag and probably frying the film that's in the camera rather than in the bag.