My character in the Champions game I currently play is a mage who has a hatred of vampires. Other than undead or demons, she refuses to kill, therefore, my GM allowed a Code vs. Killing Innocents, with the innocents in this case meaning anything that's not irredeemably evil, such as undead, demonic or the like. So vampires are okay to kill, but alien super villains aren't.
Just my 2 cents....
Rhen