There is also no objective truth in medicine. But we still let doctors decide what procedures to do, not random people with 'common sense'.

There is no true "healthy", but there is a truth about the state of your bodily function, we just do not know it whole most of times, even doctors. Physically alive and not alive is very objective.

We let doctors do whatever they suggest a lot, we also have the right to refuse medical help if deemed mentally capable. Random people with common sense decide for theirselves.