It's about being an example. It's a relatively simple solution to save Nia, but it's simplicity is exactly the reason it's fatal: No one has to die.
What does that do to a society? Remember, Genome's original status quo was developed with a similar idea in mind: If humanity stays in its place underground, under the tulage of wiser minds, they could live in peace.
We've seen how this turns out: It ends with children turned out into the wasteland, and villages turned out of their homes for progress.
We saw how society deified Kamina, and they would do the same with Simon. If not for saving their world, but for being a god himself: Those he cares for are eternal, nothing is outside of his reach.
A lot of people talk about the Spiral Nemesis, but miss an important caveat: The Anti-Spiral IS a Spiral race, and matches Simon in combat using the same kind of power: He's the sole arbiter of an species's potential, not all that different than Simon himself.
That's the other end of the road for Simon: If he insists on imposing his will against reality, he will either destroy it, or regiment it to prevent that from coming to pass.
Instead, he discards the power entirely. He will not use it for his own, and instead uses the power he can rightfully call his own. He's not Simon the deity, or Simon the hero, but Simon the digger.
Which is why his epilogue is a man and his pig roaming the wastes, drilling wells and planting flowers. It's good work, plays to his strengths, and Nia would love to have seen the greening planet. In the distance, he can watch as humanity continues forward. In case you missed the symbolism in the last shots, the Graparals form a spiral, but from the edge to the point, which is the money shot for the ideal: It's a future humans press forward, not trailing from a single point or man, but leading to it, in harmony, not unity.