Threatening people works. It works quickly to change their behavior. If a guy with a gun asks you for your wallet, you hand over your wallet. It's not because you've suddenly decided that he deserves your money but rather that you have little choice. What thoughts would be going through your mind in this situation? How would you be feeling towards the gunman?
The same ideas about threats applies with children. We can threaten them to get them to behave but it deteriorates our relationship with them. Threatening children who are misbehaving may get them to change their immediate behavior but it doesn't help them learn to make better choices in the future.