It's true that we humans need PAIN in order to grow up.
No PAIN, no GAIN!

However, do we really need people like Hitler?
Do we really need people like the emperor of China?
Yes sure, thanks to Hitler, most of the allies unite under a common cause as they're fighting the same enemy. Yes also sure, if it isn't because of the emeperor of China, China will never be united.....

But is that really the case?
In that case, wouldn't the emperor of China and Hitler be considered as a GOOD GUY if you look at it from a different perspective?

But.....
I don't believe that. Perhaps I am naive but I still do believe that we humans are capable of learning from our mistakes. Yes the things we do causes pain and also at times, causes disaster. But I believe that we are creatures that is able to learn our mistakes and repent. We are not such an irresponsible creature that we will allow ourselves to continue make mistakes.....