Antagonist

The Devil doesn't prevent you from getting what you want; instead, he corrupts your goal so it turns out uglier than you wanted, or he puts a price on it.

For example: Want to overthrow the oppressive government?
Price: You can assassinate the dictator, but it's a suicide mission, and your best friend, or your wife, is the one who'll have to do it. And you'll have to give the order.
Corrupted: You overthrow the Tsar but the Communists take over the Revolution and now you have an even more oppressive dictatorship, which you are responsible for.