Yes it is wild superstition. There is no evidence that most modern insecticides harm humans at all (some do but they are less commonly used, mostly only for specific classes of pest). DDT for example had no deleterious effect on human health, until the environmentalist idiots got it banned and malaria started killing millions again in tropical regions. The most dangerous insecticides were phased out long ago, first the arsenicals, then nicotine sulfate, both of which were very dangerous to people.

ETA: DDT was dusted directly on people for flea and lice control and typhus prevention and was primarily sprayed indoors for malaria prevention so there was a lot more direct human contact than even production plant workers have with insecticides currently.