If "life is preferable to death" were a universal attribute of all humans resulting from a biological imperative, no one would ever choose to end their life. I suspect any other proposed "universal attribute" -- at least one that take the form of a universal preference -- will fail to correspond with reality in the same way.

> all things being equal and outside of coercion.

I think that covers mental illness, war, dying in a fire while rescuing kittens, emo cutting, etc.

I don't think it covers any cases of voluntary suicide not motivated by percieved impacts on others, irrespective of mental illness. Unless you define coercion so broadly that the whole statement becomes meaningless.

>> all things being equal

If you could stop the pain without dying, would you still kill yourself?

If you could escape depression without dying, would you still kill yourself?

If you could find meaning in your existence without dying, would you still kill yourself?

If you could go to heaven (or whatever magic place you believe is better than your present situation) without dying, would you still kill yourself?

If you could kill yourself without dying, would you still kill yourself? (Weird I know, but for the sake of completeness)

Did I miss any good reasons to kill yourself?

Please provide a single example of when "all things being equal and outside of coercion" (using your extremely broad definition of 'coercion') a human made a choice to live rather than die.

Or is your 'universal attribute' some sort of 'ideal' that doesn't actually ever happen and thus is completely useless for defining the set of 'human' and 'not human', let alone 'moral' and 'immoral'.

Sure, you woke up and didn't kill yourself. As did most every human being that has ever existed, because humans don't do that outside of very strange circumstances that are out of their control.