When you were growing up was everyone afraid of tampered candy during Halloween? Growing up in Wisconsin, our local police force volunteered their scanner to ensure no metal was in our candy. What was up with that? How could anyone have ever believed this? We thought that there were people out there with enough smarts, resources and child hatred to take chocolate bars out of wrappers, insert razors or inject poison, then somehow seal them back? And these people are thinking, "I'm going to put a lot of time and energy into hurting random children who have the audacity to beg for milky ways. And this is despite the fact that I am one of only 20-30 houses they hit up, and so this crime will easily be traced to me. This is the perfect crime."
Obviously, it's an urban legend, but it's amazing that so many people believed it, and in some cases, continue to believe it.