Gene Wolfe on the Spartans

Yes, The Spartans were the most totalitarian people that I have ever come across. They made the Nazis look like Boy Scouts and they really did it, and they did it for it for a hundred years and they were so totalitarian as to be almost unbelievable. One of the strange things about Sparta was they had the two kings and I am sure you realize. [...] One of the strange things is that the kings really represented the good past in Sparta. They were relics from the time when Sparta was a Greek state much like other Greek states. They were slowly being constricted and crowded out by the totalitarian ethic.

(Gene Wolfe, in an interview)

I would like to hear Wolfe's opinion on Frank Miller a Zack Snyder's 300...

By the way, in that same interview, a bit after the passage I quoted, Wolfe mentions a very nasty thing the Spartans did after Thermopylae (warning: it's a bit of a spoiler for Soldier of the Mist):

when the Spartans were fighting the Persians, they were fighting them with their light infantry, and their skirmishers and so forth were bands of armed Helots. At the end of the war they said, we are going to reward you Helots by giving those who did most in the war their freedom. And they will be not equals __________who would be able to run for office and vote and so on and take part in the government but they would be free individuals living in Sparta and free as such people were. And so you are to name for us those Helots who were your leaders in the late war who should be rewarded like this. Then they held a ceremony which I described in detail, exactly as it was and they gave each Helot who was to be awarded his freedom as a climax of the ceremony a young Spartan as his companion to lead him through the ceremony. And at a given signal each companion killed that Helot that he was responsible for. And they were all killed [...] and all of [...] them who had gone in the ceremony were butchered. And they really were, this took place.

What classical sources mention that episode? I don't remember reading about it in the works of Herodotus or Thucydides.