Jimahl is spot-on. True, there will always be evil in the world, but what would this world be like if we didn't fight back? Sure, Hitler was followed by the U.S.S.R and Al Qaeda, but if we hadn't fought the Nazis, think what the world would be like! And furthermore, it is our duty as human beings to fight them. It's the right thing to do, and it's always right to do what's right because ti's right. That's the point of getting rid of evil.
What's the point of using an umbrella if it is only going to rain again? Sorry, but your question is just ridiculous. A tyrant should never just be ignored simply because there will be another one in the future. You fight against the evil because it is the right thing to do. So we can protect people from that evil.
How do you know that? Thomas Edison found 2000 ways not to make a light bulb before he found one way that worked. Why stop when it could be the very next attempt?
Also, submitting to evil is not something I can do. It violates by personal ethics.
Another evil will arise regardless of whether or not one is destroyed. Better one less then one extra. ^^
The sense of accomplishment!
Maybe he'll be less evil :P