If misbehavior is unintentional,why is it punished?

If it was unintentional but due to carelessness, then it is punished due to the carelessness.

If you run a red light accidentally, or on purpose, you could still cause injury or death.

similarly, even if there is intentional misbehavior, such as cheating on taxes, why does the person have to give the money back AND go to jail?

It seems like you shouldn't have to do both.

Either give back the money, or go to jail.

Wesley Snipes got screwed big time. He gave back all the money he owed, PLUS 3 million in extra fines, PLUS 3 years in jail.

The government is profiting from criminals.

To whom are you referring too? children or adults. I don't know if they consider misbehaving by an adult even feasible,it's more of a child thing don't you think.

So you don't do it intentionally later because u got away with it when it was accidental.

So you learn not to do it again and the idea of consequence.