OK, let's say the person making "profit" is a doctor, and you're going to take everything he makes over a defined amount as tax.
Once he hits that limit - say, on July 1 - is he even going to work any more? Will ANY person - doctor, lawyer, nurse, plumber, electrician, carpenter, whoever - continue to work once they hit the point where 100% of their earnings will be taxed at 100%?
Good luck getting ANY goods or services late in the year.
"The stupid, it hurts."