Problematic At a Minimum
What if I share with my doctor that I use illicit substances? Could the police use that info to secure a search warrant for my residence, so they could arrest and imprison me?
What about if I share that I'm gay, for instance if I had HIV, could a future authoritarian regime then come after me for persecution?
Just two instances that I thought of, I'm sure there are as many reasons to keep one's medical info private as there are people needing medical care. It's a bad idea all around.