This is an is/ought confusion. You can explain why something is that way, but you can't explain why it must be that way.
You can explain why our survival instinct evolved so it is tempting to jump to the conclusion that we ought to survive but it is a fallacy (called the naturalistic fallacy): saying that something being natural means it is good.
You can explain why our survival instinct evolved so it is tempting to jump to the conclusion that we ought to survive but it is a fallacy (called the naturalistic fallacy): saying that something being natural means it is good.