I've already explained above why a legit sick day is important, it stops your staff having to choose between being paid and doing the right thing - not spreading the illness.

Unscrupulous business owners demanded too much of their staff, including working whilst sick - so the law was changed so that those staff would be protected.
Unscrupulous employees abused this, so a limit was put in place - you get ten days a year.
But somehow, you've decided that a staff protection is actually extra days off, that are being stolen from you if you don't get sick!
"in your own head" as you put it.

I'm not currently managing a team, but when I did, I never asked for a sick note from the doctor, what a waste of time and money.
People with your sense of entitlement cause nonsense like that.

No one is entitled to your work for free.
You aren't entitled to payment for nothing.
There's a balance here, ever changing, with sloppy vague laws applied post facto in an effort to maintain it.
I'm not against changing it, but taking your sick days as unplanned leave is against the spirit in which those sick days were bargained.