Should the DMV screen for mental health conditions?

They already screen for other physical conditions that would affect your ability to safely drive a car. Why are people hesitant to go down this slippery slope of screening for mental health conditions? Do they honestly believe that mental health conditions would not affect someone’s driving ability?

My sister is schizophrenic and the DMV renewed her license with just the written test. It scares the crap out of me that she can legally drive a car.

And it should scare you too.

Inspired by some discussion from another question.