It’s my theory that the sub-minority persecution has two sources. The first source is illustrated in Robert A. Heinlein's "Stranger in a Strange Land" where Valentine Michael Smith learns why humans laugh:
But today even the misanthropy of camels could not shake Mike's moodiness. Nor did monkeys and apes cheer him up. They stood in front of a cage containing a family of capuchins, watching them eat, sleep, court, nurse, groom, and swarm aimlessly around, while Jill tossed them peanuts.The moral of the story is that abuse is transferred. Minorities will find sub-minorities to persecute just as the minority is persecuted.
She tossed one to a monk; before he could eat it a larger male not only stole his peanut but gave him a beating. The little fellow made no attempt to pursue his tormentor; he pounded his knuckles against the floor and chattered helpless rage. Mike watched solemnly.
Suddenly the mistreated monkey rushed across the cage, picked a monkey still smaller, bowled it over and gave it a dubbing worse than the one he had suffered. The third monk crawled away, whimpering. The other monks paid no attention.
Mike threw back his head and laughed - and went on laughing, uncontrollably. He gasped for breath, started to tremble and stink to the floor, still laughing.
The second source of persecution is the embrace of purity by the minority. Consider that the minority is persecuted for a specific quality. The majority attempts to condemn the minority for the quality. The minority responds by embracing that quality, transforming it into something that is honored. This is commendable. The shadow side is that the quality is honored to such a degree that a standard of purity is established. People must meet this standard to be a qualified member of the minority.
The two sources combine. The need to persecute a sub-minority is augmented by standards of purity within the minority. To reference Heinlein's story, the mistreated monkey looks for a target. The easiest targets are those people who are mostly in the minority, but not quite due to some variation of quality. The third monkey is identified and given a vigorous dubbing.
Is persecution of the sub-minority a forgone event? Can the minority learn from it’s own circumstances? I don’t know. I wonder if this an inevitable part of life. Time will tell.