Exactly. PTO is simply time off, we do not need to explain ourselves. My basement could be flooded, I could be sick, I could still be out partying from the night before or maybe I just don't feel like showing up. no one's business.
My company used to be like that -- we never had "sick time" accumulation, and if we were sick or on vacation, the time off came from the same PTO bucket that we had earned.
However, a few years back they changed things up a bit. They reduced the amount of PTO we earned in a year by 5 days. BUT, we no longer have to take PTO when we are sick. In fact, no "sick leave" was accumulated -- we just take time off and it is never accounted for in the books. It is now up to your manager to monitor if you are abusing this benefit. With no "sick time" on the books, it makes the financials look better (no liability that needs to be carried on the books for years).
Another big benefit is that people who are not feeling well and may be contagious are less likely to come into the office and infect others. When you have to burn your own PTO, you are more likely to "tough it out" in the office, which may result in lower overall productivity as others may get sick as well.
So when someone here takes a "mental health" day, it is simply a day off, and their earned PTO is not reduced. The managers need to ensure it is not abused, but a mental health day once or twice a year is not frowned upon. (Now, it if was every Friday during summer...)
This works well in my work environment: an R&D lab, where everyone is salaried. When our schedules are put together for a project, we always estimate some amount of time for vacations, etc., so there is no "emergency" or "double shift" needed when someone is out sick. I know several companies in my industry that have similar policies.
Kurt