thank you for your commenting all. But now I realized that "this kind of Perfect Government" and "less human behavior is actually possible in the world of Trek. But don't think that I will give the credit to human. No, humanity changed not because they realized their mistake after WWIII. The reason is too naive.
I think, the most logical reason is that because they are being exposed to many Alien cultures. Look at us, we love to copy other people behavior. So, what prevent us to mimicking Vulcan?
Come on, who can resist Vulcan? Look at them. Even with nerd hair cut and naive eyes, Vulcan is actually a bad ass. They can kick their enemy around with only touch their shoulder. And they clever like hell. No human children could win a science competition against Vulcan. That's why Vulcan can become the role model of some people.
And because they interact closely for more than three centuries, it is possible that some human has become more "Vulcan" than their ancestor. I think, it is the most possible answer for this problem.
Why human is so weak and easily to exposed by more advanced cultural entity? We have some examples in real life. Look at Japanese. They are more American than their ancestor now. And not only them, there are a lot of cultural transfer and change of behaviors in our world. Some because of culture, other because of religion. That's why the human in 24th century is also exposed and maybe influenced by the foreign culture, like Vulcan, or Klingon, or Romulan, or the others. It is a natural way of life in our universe.