The ethics of existential risk concerns the questions of how bad an existential catastrophe would be, how good it is to reduce existential risk, precisely why those things are as bad or good as they are, and how this differs between different specific existential risks. There are a range of different perspectives on these questions, and these questions have implications for how much to prioritise reducing existential risk and which specific risks to prioritise reducing.

In the effective altruism community, the ethical perspective most associated with existential risk reduction is longtermism: existential risks are often seen as a pressing problem because of the astronomical amounts of value or disvalue potentially at stake over the course of the long-term future. But other ethical perspectives could also lead to a focus on existential risk reduction.

For example, in The Precipice (Ord 2020), Toby Ord discusses five different "moral foundations" for the importance of existential risk reduction:

• The present: Many existential catastrophes would involve death and suffering for vast numbers of people alive at the time it happens.
• The future: An existential catastrophe would destory of humanity’s longterm potential.
• The past: We could see humanity as a vast partnership across time, and an existential catastrophe could be seen as "fail[ing] every generation that came before us" (Grimes 2020).
• Civilizational virtues: "by risking our entire future, humanity itself displays a staggering deficiency of patience, prudence, and wisdom." (Grimes 2020)
• Cosmic significance: "this might be the only place in the universe where there's intelligent life, the only chance for the universe to understand itself, on how we are the only beings who can deliberately shape the future toward what is good or just." (Grimes 2020)

The "present"-focused moral foundation could also be discussed as a "near-termist" or "person-affecting" argument for existential risk reduction (Lewis 2018). In the effective altruism community, this is perhaps the most commonly discussed non-longtermist ethical argument for existential risk reduction. Meanwhile, the "cosmic significance" moral foundation has received some attention among cosmologists and physicists concerned about extinction risk.

However, it is important to distinguish between the question of whether a given ethical perspective would see existential risk reduction as net positive and the question of whether that ethical perspective would prioritise existential risk reduction, and this distinction is not always made (see Daniel 2020). One reason this matters is that existential risk reduction may be much less tractable and perhaps less neglected than some other cause areas (e.g., near-term farmed animal welfare), but with that being made up for by far greater importance from a longtermist perspective. Therefore, if one adopts an ethical perspective that just sees existential risk reduction as similarly important to other major global issues, existential risk reduction may no longer seem worth prioritising.