Either not dying is more than a preference (and your point is invalid), or it is a preference (and there is no rational reason to prefer continued existance over dying).
Well, I think that's a matter that fits under the "no religion" rule, and we shall simply have to agree to disagree.
Preferences are emotive.
A preference is a true statement.
In a logical system, there are two forms of true statements. One type is an axiom - these are statements that are assumed to be true, and so cannot be logically proven, or argued against - though it can be shown that some systems of axioms are inconsistent. Emotive preferences might be akin to axiomatic statements.
However, for your archetypal logical system, there are an infinite number of quite logical statements that follow as true, once you assume the axioms. In fact, no logic can be undertaken *until* you assume the axioms.
So, if we assume that my wife prefers to live as an axiom, then the preference to avoid strawberries follows from pure logic. The two statements, are not equivalent, but one follows from the other.
If the GM and player agree upon their axioms, then showing the logic behind other preferences can lead them into agreement, or to suitable compromises.
I can imagine the outrage if it were suggested that players be required to defend their preferences in making characters they want to play!
Well, I think you're upping the ante with, "required".
They'd be outraged if you insisted they justify every tiniest detail, sure. But asking them for reasons behind a choice or two that seemed to be outside what we'd set as an expectation to start with? That should not be an issue with a reasonable player.
I get to ask some things as GM, they get to ask some things as players. Sounds even and fair to me.