I think that phrase is right “to zeroth order”: one can imagine an agent with any preferences about population ethics. Then “to first order”, I think the choice between average vs total utilitarianism does have a right answer (see link in my reply to Cleo). And then there are “second order” corrections like value of variety, which seem more subjective, but maybe there are right answers to be found about them as well.
I think that phrase is right “to zeroth order”: one can imagine an agent with any preferences about population ethics. Then “to first order”, I think the choice between average vs total utilitarianism does have a right answer (see link in my reply to Cleo). And then there are “second order” corrections like value of variety, which seem more subjective, but maybe there are right answers to be found about them as well.