Flame wars usually happen of other types of simple questions, such as "What's better, Pathfinder or 4th Ed Dnd?" or "How can I engineer a TPK without my players knowing?" The easiest policy is just not to discuss those topics here, make it someone else's problem. I like your question though. I think it's the allure of doing something you wouldn't do in real life, exploring you darker nature as it were. A friend of mine had a brilliant idea about this once that I totally am going to steal at some point. Step 1: Have an evil campaign. Keep track of everything that is done for later. Step 2: Create a good campaign with the same players tasked to clean up the world, with their old characters as the Big Bads. Step 3: Profit!