You are comparing apples to oranges. The majority of Cessna 172 pilots
are not flying for hire. I do not have a problem with for-hire pilots
needing a medical.

You can drive a heavy truck with a regular drivers license. You don't
need a medical or a CDL.

Drug and alcohol tests for pilots are fine too. There is clear evidence
that shows that driving/flying under the influence is dangerous to the
public. However, there is no overwhelming evidence that a pilot with a
blood pressure 20 points higher than normal is so much of a hazard
that they should be barred from flying.