Here a few excerpts to illustrate how Aldous Huxley predicted a decline of monogamy in Brave New World (our world?). I believe that "How can you be stable if you are feeling strongly?" says it all:
Family, monogamy, romance. Everywhere exclusiveness, a narrow channelling of impulse and energy.
"But every one belongs to every one else," he concluded, citing the hypnopædic proverb.
The students nodded, emphatically agreeing with a statement which upwards of sixty-two thousand repetitions in the dark had made them accept, not merely as true, but as axiomatic, self-evident, utterly indisputable.
"But after all," Lenina was protesting, "it's only about four months now since I've been having Henry."
"Only four months! I like that. And what's more," Fanny went on, pointing an accusing finger, "there's been nobody else except Henry all that time. Has there?"
Lenina blushed scarlet; but her eyes, the tone of her voice remained defiant. "No, there hasn't been any one else," she answered almost truculently. "And I jolly well don't see why there should have been."
"Oh, she jolly well doesn't see why there should have been," Fanny repeated, as though to an invisible listener behind Lenina's left shoulder. Then, with a sudden change of tone, "But seriously," she said, "I really do think you ought to be careful. It's such horribly bad form to go on and on like this with one man. At forty, or thirty-five, it wouldn't be so bad. But at your age, Lenina! No, it really won't do. And you know how strongly the D.H.C. objects to anything intense or long-drawn. Four months of Henry Foster, without having another man–why, he'd be furious if he knew …"
"Of course there's no need to give him up. Have somebody else from time to time, that's all. He has other girls, doesn't he?"
Lenina admitted it.
"Of course he does. Trust Henry Foster to be the perfect gentleman–always correct. And then there's the Director to think of. You know what a stickler …"
Nodding, "He patted me on the behind this afternoon," said Lenina.
"There, you see!" Fanny was triumphant. "That shows what he stands for. The strictest conventionality."
Lenina shook her head. "Somehow," she mused, "I hadn't been feeling very keen on promiscuity lately. There are times when one doesn't. Haven't you found that too, Fanny?"
Fanny nodded her sympathy and understanding. "But one's got to make the effort," she said, sententiously, "one's got to play the game. After all, every one belongs to every one else."
"Yes, every one belongs to every one else," Lenina repeated slowly and, sighing, was silent for a moment; then, taking Fanny's hand, gave it a little squeeze. "You're quite right, Fanny. As usual. I'll make the effort."
No wonder these poor pre-moderns were mad and wicked and miserable. Their world didn't allow them to take things easily, didn't allow them to be sane, virtuous, happy. What with mothers and lovers, what with the prohibitions they were not conditioned to obey, what with the temptations and the lonely remorses, what with all the diseases and the endless isolating pain, what with the uncertainties and the poverty–they were forced to feel strongly. And feeling strongly (and strongly, what was more, in solitude, in hopelessly individual isolation), how could they be stable?