Say someone scammed you or someone you know and you know you can scam them back.
If I found out that someone deceived me, I would not deceive him in return. I would simply expose him, preferably in public. So that everyone would know that he is a deceiver. And if I deceived him in return, I would become a deceiver like him.
You would do exactly the same I would do. Especially here on bitcointalk, we has to alert the community about scammers to keep the community clean.