Prator the Legendary
Getting away scotch-free? Are you referring to the whiskey, or the brand of tape? Or perhaps hop-scotch? Why would you want to be free of any of those things?
I think it's an interesting idea, but it's not one that I'd likely use for any of my own villains, mainly because there's usually some alternatives which work better and don't involve as much personal risk. For example:
1. Making an Enemy: Quite simply, you pick ANY group you can find that is idealogically opposed to your/your country's/your group's values, and then declare war on them, claiming that their very existence is a threat to you/your country/your group (bonus points if you can make it look like they perpetrated some act of war on you first). Try to unite as many other factions as you can against this one faction. The main problems with this approach is that your newly-made enemies will likely respond with the same tactics, and if you ever WIN the war, your united world might divide again without a common enemy. Cold War, anybody?
2. Unite by Force: The Roman approach to conquest (I believe the early Persian and Islamic empires did this too...). In a nutshell, you gather an army and take over another country/group, and then conscript the newly conquered people into your army so you can fight more/larger foes. It's extremely effective if you have time to let the new guys settle in, but you can't really run a blitzkrieg war this way.
3. Unite by Dogma: The classic kind of Jihad, which the early Islamic Caliphates were very famous for. Your goal is to unite everyone, and you approach this goal from two directions. First, there is a war of information: develop a religion or other ideology that large numbers of people will want to get behind, and attempt to spread it by word of mouth and other means. When simple conversion fails, you may proceed to conversion by the sword. Again, this approach requires time to work. Also, you find that people will try to counter you using #1.
...Uniting everyone by making YOURSELF a common enemy to all is unlikely to work if you can't do it properly and extremely dangerous even when you do it perfectly. The only circumstances in which I can see a person justifying that means of unification are those where there is an immediate threat to humanity that demands a swift and cohesive response... but if you have an immediate threat, why not resort to #1?