Necessary, because if it were not true — if the fact the appetite for space exploration cannot be satisfied in the near future has NOT created a gap between reality and anyone’s expectations — then we have no reason to think science fiction creates dissatisfaction. Without (A), the author’s argument does not establish that there’s a gap between expectations and reality.

Not necessary, because the argument isn’t weakened if science fiction has created unproductive dissatisfaction in other ways unrelated to the appetite for space exploration. The author assumes that ONE way science fiction has created an unproductive dissatisfaction is through creating the appetite for space exploration; but the author doesn’t have to think it’s the only way.

Not necessary, because the argument is based on a particular appetite created by science fiction — the appetite for space exploration. Whether other appetites can or cannot be satisfied doesn’t change the fact that the appetite for space exploration cannot be satisfied in the near future.

Not necessary, because the argument is based on the fact that science fiction has created an unsatisfied appetite for space exploration “among certain people.” The author doesn’t have to believe these “certain people” constitute over half of people (”most”) in the world.

Not necessary, because the author argues from the fact that certain appetites are NOT satisfied to the conclusion that science fiction has created unproductive dissatisfaction. This doesn’t require any assumption about what would be true if appetites CAN be satisfied. Nor does this require any assumption about what would be sufficient to prove that science fiction could NOT create an unproductive satisfaction. (If the author’s trying to prove A → B, that doesn’t require the assumption that Not A → Not B.)