The food and drug administration has deemed mass-produced consumer food items as safe to eat provided they have an acceptable percent of non-toxic contaminants in them. Insects, a worker's finger or hand, etc. are all considered acceptable ingredients if they constitute below a certain percentage in the overall batch.
Why? Because they don't pose any sort of realistic health risk to the general population. Food is processed to eliminate bacterial or viral contaminants before being shipped to stores.
I'm comfortable with it, especially since Reeses is the only candy worth eating. This one time though, I opened a fig newton and observed a live maggot on it writhing just in time to spare an untimely demise via incisor. My inability to eat another fig newton since is just an added bonus. Stupid youngness and susceptibility to trauma. >: (