Most pesticide exposures occur without peoples' knowledge or consent. Virtually all foods, medicines, personal hygiene, cleaning and household products list ALL ingredients on product labels. Pesticides do not stay where they are applied. They drift, runoff, volatilize for extended time periods, get tracked and are spread around by sweeping or mopping. Pesticides are harmful to many non-target organisms, including humans and other beneficial species.
Pests quickly build up resistance.
People do not. Chemicals should never be your first defense against pests. Ineffectiveness leads to repeat exposures. Even beer and tobacco cannot be sold for pest control purposes, wear labels or attached pamphlets telling how to use them to kill certain pests - without first registering them as pesticides. There is no reason to assume pesticides are safe.