Except that some people think they actually know better than doctors, take things to an extreme and cause themselves and others serious harm.
It's horribly sad when people are convinced they can cure their cancer with some sort of natural remedy or unusual health regime, and end up not only not being cured but maybe dying much sooner than they would have done.
It's even sadder when parents harm their own children by subjecting them to an extreme diet - vegan or macrobiotic or whatever - which children can't digest properly and which lacks vital nutrients. Even when the child is visibly sick and in need of emergency medical treatment, they still insist the diet is health-promoting and refuse to give it up.
I just wonder how anyone can be so stubborn and so irrational as to pursue a self-chosen "treatment" based on nothing but subjective belief.
A Florida mother who fed her three children on a strict vegan diet of raw fruit and vegetables was jailed for life for killing her 18 month old son. He was severely malnourished and weighed only 17 pounds (8 kilos) when he died.
If I had some severe illness, I would never presume to know more than the doctors and pursue some eccentric regime I'd seen on social media or heard someone gossiping about. I'd assume the doctors knew better than me, even if they might sometimes get things wrong.
Self medication has its limits.