Though in his "Movie Memories" book, Shatner reports some conflict between Nimoy and producer Harve Bennett over whose movie this was going to be, at the beginning of the process the two came to a series of conclusions in fairly short order. Nimoy wanted a lighter tone; after the death and destruction of the previous two movies, it was time for a grand adventure. He believed that many of the best Star Trek episodes did not involve the good guys confronting the bad guys, so they agreed on a film without villain or violence.

It doesn't appear they considered simply starting a new story at a time well after the events in III, so they made at least a de facto decision to complete the trilogy begun in Trek II, making the action continuous with the events in the previous two films. They also agreed on the basic device of time travel, and they soon became enamored with the idea of bringing the 23rd century crew back to earth in the 1980s.

The story question then became, why? The returning crew could be dispatched through time against their will, and then they either discover some problem to solve in that past, or simply struggle to return to the 23rd century without damaging the time line. Or they could go back intentionally---if they had a reason. What would that reason entail in a Star Trek story? In the DVD commentary, Nimoy puts it this way: "What would be lost in the 23rd century as a result of the unconsciousness of the 20th?"

This kind of reason alone reflected Nimoy's vision of Star Trek, which despite some personal and professional conflict, kept faith with Gene Roddenberry's basic vision.

The direction towards an answer came from "Biophilia," a book by biologist Edward O. Wilson that Nimoy was reading. "Biophilia" as Wilson defines it, means the innate "emotional affiliation of human beings to other living organisms." It is both a hypothesis about the natural disposition of humans to feel deeply and intrinsically a part of the natural world, even when alienated from it by the cement and smog of modern life, and an ethic, promoting the possibility of that relationship by giving priority to making sure than other species of living beings have what they need to live.

But as Wilson noted, human civilization is mindlessly obliterating other life on this planet, and forcing the greatest era of mass extinctions in 65 million years. Wilson goes beyond typical environmentalism to ask whether other life has an innate right to exist that is equal to the moral rights of humanity. Answering this question in the affirmative was an implied foundation of Star Trek's approach to life in the universe, which became more and more explicit in the 1980s, especially in Star Trek: The Next Generation. Still, the basic insight of ecology pertains here: humanity is embedded in the life of the planet, and cannot survive without it. By destroying other life now, humanity is destroying itself in the future.