"Don't lose your temper," said Ruell evenly. "It's your worst fault, except for ignorance." - Damon Knight

Voluntary birth control methods only work on the people who choose to use ’em. A population check that doesn’t work on everybody doesn’t work at all, because it simply breeds out the ones who use it. The only population check that really works is one that affects everybody, like a limit of space or food.

A society that put more emphasis on birth than ability was likely to breed ability out of its ruling class.

He was going to die. His mind flinched back in horror from that, but it was still there, grinning, implacable. His body would rot under the ground, while delicious things were still happening in the sunlight.