After watching the long-ass eternal movie, I began to ponder on these questions 
Was killing the celestial Tiamut, right? 
Are the Deviants evil?
Are Celestials evil?
Who did the right thing?

The movie spoke about how Celestials are very important to the survival of everything living in the galaxy or galaxies, including humans, animals, etc. The importance of the Celestials should be emphasized because, without them, everything dies literally, and this reason, not majorly but still, justifies why Tiamut should be left alive.

Arishem said, "The end of one life is the beginning of another"

The Emergence is a revolutionary process that creates life, i.e., the birth of Celestial Tiamut or any other Celestial has to feed on intelligent life for that to happen. This means for new galaxies to be formed, for evolution to happen, a Celestial had to be born, and many would-be sacrificed, but Earth prevented this from happening, and it was wrong.

Humans are best known for doing anything to survive, to protect themselves from harm even when it affects another form of life. Take, for example, eating; humans have to kill animals to eat; hence the survival of the human race depends on other living things. What would happen if the animals and plants come together to fight off humans and prevent them from eating, the answer is simple humans will simply look for another alternative or die. The best suitable option is to go to war with animals and plants or eat themselves (Humans eating humans). This could be equated with the situation of the celestial and Eternals. Humans are also part of the evolutionary process that allows for new Galaxies to be formed; in fact, that we have humans shows that trillions of years ago, a Celestial would have killed billions of living things from another Galaxy or planet; hence it is unfair for Eternals to stand their ground or go against the process.

The deviant, on the one hand, we're smart; they knew what would happen if intelligent life grew to the extent of allowing Celestials growth. But they prevented it, and this is because if a Celestial is born, they die too and go into extinction.

"We have helped the Celestials expand life across the universe, that's not what bad guys do, that's what good guys do," Kingo said this in the movie. It proves that what they did wasn't wrong, but maybe they shouldn't have been manipulated by the removal of their memory and telling them there were from Olympia. Still, then if they were asked to make their decision, they would choose to defile the Celestial anyways; even after the manipulation, they still did.

"Sersi, we have no right to stop the birth of a celestial" Kingo

I think even Immanuel Kant would also agree with this view. Immanuel Kant, the founder of Deontology ethics, believes that an action is considered morally good because of some characteristic of the act itself, not because the result of the action is good. In this case, the action was the death of Tiamut, and the result was humans got to live.

In another instance, a Consequentialist would have supported the greater good, which is for a 
Celestial to be born and create more galaxies where trillions of life would be born. Because a consequentialist weights the result of an action, allowing Tiamut to be alive would overturn the activity that helps humans survive.

I hope you enjoyed the read. If you have another opinion, please write about it, and I will love to read it.