For me, it's past experiences with doctors. Trusted them, got a surgery that they said would be beneficial, they tortured me with inadequate anesthetics, had complications lasting years, and found out afterwards that the procedure was totally unnecessary and the ostensible harm it was meant to preempt was very unlikely and would have been a much less extreme procedure. Still have the scars. I look at American doctors living in big houses, hear other stories like mine, and connect the dots. They recommend procedures to make themselves money.