No, that'd make for a terrible story. Wow. Some guy is a good guy. Nope. He's not. The end. There is little to build off of. No hope for the future, no nothing. Just because an idea is fun to toy with, it does not really mean that the idea would make for a great story. In Harry Potter, someone could've used a TimeTurner to kill Voldemort as a child. Sure, it'd be amusing, intriguing, and entertaining to think about. In practice, though, it'd be terrible for the plot.