You're thinking of "The Highest Treason," a novella by Randall Garrett. (First published in Analog -- January, 1961). It turns out that Garrett never renewed the copyright, and thus the full story is now archived, in several formats, on Project Gutenberg.
Your summary from memory was good enough to let me recognize the story right away. But it's worth mentioning that the human "traitor" actually went the Benedict Arnold route by becoming a commissioned officer in the armed forces of a militaristic alien race that wanted to conquer us all. He encouraged them to slaughter the entire population of one colony world (about 150,000,000 people) as a show of force to terrify the billions of other humans into meekly submitting to superior military force so the same thing wouldn't happen to them.
What the protagonist knew perfectly well, but the aliens didn't, was that such terror tactics could easily backfire. And the repercussions could cause some drastic changes in a society which he felt could not be forced to change by any lesser stimulus than the shock of knowing that a planetary population had just been annihilated and some new ideas were needed in a hurry!
Here are a few quotes from the story to illustrate that it's the one you had in mind. The first passage quotes a portion of an explanation (offered not by the protagonist, but by an omniscent narrator, apparently) of how and why human society has become obsessed with "equality."
Society had decided that intolerance and hatred were caused by
inequality. The jealousy of the inferior toward his superior; the
scorn of the superior toward his inferior. The Have-not envies the
Have, and the Have looks down upon the Have-not.
Then let us eliminate the Have-not. Let us make sure that everyone is
Raise the standard of living. Make sure that every human being has the
necessities of life—food, clothing, shelter, proper medical care, and
proper education. More, give them the luxuries, too—let no man be
without anything that is poorer in quality or less in quantity than
the possessions of any other. There was no longer any middle class
simply because there were no other classes for it to be in the middle
This next passage is found much later in the story. Sebastian MacMaine (the protagonist) is explaining, as best he can, what he felt was terribly wrong with his native culture (which was essentially the same culture for all human beings, on Earth or any of its colonized planets):
"Earth was stagnating," MacMaine said, surprised at the sound of his
own voice. He hadn't intended to go on. But he couldn't stop now. "You
saw how it was. Every standard had become meaningless because no
standard was held to be better than any other standard. There was no
beauty because beauty was superior to ugliness and we couldn't allow
superiority or inferiority. There was no love because in order to love
someone or something you must feel that it is in some way superior to
that which is not loved. I'm not even sure I know what those terms
mean, because I'm not sure I ever thought anything was beautiful, I'm
not sure I ever loved anything. I only read about such things in
books. But I know I felt the emptiness inside me where those things
should have been.
"There was no morality, either. People did not refrain from stealing
because it was wrong, but simply because it was pointless to steal
what would be given to you if you asked for it. There was no right or
"We had a form of social contract that we called 'marriage,' but it
wasn't the same thing as marriage was in the old days. There was no
love. There used to be a crime called 'adultery,' but even the word
had gone out of use on the Earth I knew. Instead, it was considered
antisocial for a woman to refuse to give herself to other men; to do
so might indicate that she thought herself superior or thought her
husband to be superior to other men. The same thing applied to men in
their relationships with women other than their wives. Marriage was a
social contract that could be made or broken at the whim of the
individual. It served no purpose because it meant nothing, neither
party gained anything by the contract that they couldn't have had
without it. But a wedding was an excuse for a gala party at which the
couple were the center of attention. So the contract was entered into
lightly for the sake of a gay time for a while, then broken again so
that the game could be played with someone else—the game of Musical
I have serious doubts about whether the entire human race, while inhabiting many separate planets (even if they all had a common governing structure that tried to dictate educational policy for the children) would ever embrace the mindset and lifestyle that MacMaine is describing. But Garrett makes it seem plausible (or nearly so) to the reader at the moment he or she is first reading it, and I remind myself that he was deliberately taking certain ideas to extremes for dramatic effect.