Tom,
I agree, it is largely a matter of perception, and that a birthday cake where the person blows out the candles is likely to be more dangerous whereas a pizza will be subjected to oven heat that will kill anything that might be harmful. Offhand, I do not ever recall someone refusing to eat a piece of a birthday cake because the person blew onto the cake when blowing out the candles. It's also quite natural that a person such as yourself who has been sensitized to the many unhealthful practices in the food industry over most of your life and work career, along with endless regulations, to be more careful, and also more aware, than most of the population.
Peter