There's two guys on the street both alike but pretty different in an important way.
Both guys here are on someone's payroll. But the difference is in how much gets taken out of their checks. The guy on the left makes $225,000 while the guy on the right makes $115,000.
The guy on the left makes $225,000 so he loses 1.45% cause of Medicare then 2.35% which is more than the guy on the left who only makes $115,000 and gets 1.45% taken for Medicare. This tax only affects people who earn wages and their employers.
Medicare just pays our hospitals and the costs from people with Medicare i.e. older people who are 65 and older and young people with disabilities.