Everyone worth arguing with already understands that we're not going to get to 0% evil through voting. Evil people don't become good just because people want them to, and the same goes for the evil organization that puts forward all of these evil candidates.
In a working system voting can help stave off evil, but it can't remove it once the system is broken and evil has taken hold. All we can do through voting now is pick our enemy, and it's easier to fight a 20% evil guy than a 100% evil guy.
Sure, you can make the argument that we'll never fight either, and it's not a bad guess, but if we don't then we just have no avenue for success, so I'd rather be ready for a revolution I have no faith in than just give up.