When you are traveling to an unknown world, setting out on a quest, battling monsters of any stripe, you want to be able to keep your family safe in a place far, far away. Perhaps, in fact, you travel/quest/battle in order to do just that.
Science fiction, as a literature of escape, often defines escape as leaving the notion of nuclear family behind.
Why does the idea of nutritive pills hold appeal when so much pleasure is derived from eating? Popping pills implies an escape from the family dinner table.
Why does the idea of cloning hold appeal when so much pleasure is derived from current reproductive practices? Cloning implies an escape from the two-parent family.
With time travel, everyone you know is either dead or unborn. With single-gender societies, you've effectively erased your most difficult relationships. With virtual reality, you've lost all notion of blood-ties. With aliens, you've managed to turn your back on the human race.
Science fiction, as a product, is manufactured by a person working within a cocoon. Outside of that pod of isolation, parents, partners, and children are clamoring for the writer's attention. The writer imagines a world where there would be freedom from those pressures.
Imagine a world where I would be free from the horror of my mothers's alzheimer's, my partner's insistence that I paint the kitchen, my children's never-ending hunger for attention. Imagine the world free from the baggage of awkward silences or the alternate which is often worse.
My father's disappointment. My partner's bitterness. My child's rebellion.
Imagine a world.