There are generally three arguments I've heard against the practice of irradiating food. One is that the irradiating process will somehow chemically change the food and make it unhealthy. Another is it might create some mutant bug that will destroy Tokyo. The third is that companies will rely on irradiation to the extent that they will use more dangerous food handling procedures. All of these arguments are bunk.
Yes, the process will chemically change the food. So does cooking. I guess the idea of cooking is "unnatural" and should be stopped at once. As for mutating bugs, that's why they use lethal doses--sub-lethal doses would be a bad idea. And as for the third argument, does pastuerization mean dirtier dairies? Compare a dairy today to one 150 years ago.
The real problem (as usual) is the one no one seems to want to talk about: It is dangerous to try to shield humanity from microbes that have always been in the environment.
The trend in marketing these days is to throw tons of anti-biotics into every consumer item (toys, diapers, sponges, even pillow cases). With better epidemiological investigations (thanks to lawyers), the media is filled with scary stories that suggest YOU ARE NEXT! Marketing fear has always been an easy sell.
But if we successfully sterilize everything in our environment, the very first free germ will wipe out our entire civilization. It is impossible to achieve perfect sterility but the more we hide from the environment, the more we have to hide. And trying to hide means more and more anti-biotics that are more and more powerful. This is a recipe for disaster: resistant strains and worthless drugs.
I oppose irradiation not because it won't kill off germs, but because it will.