  How should we think of the preferences of citizens? Whereas self-optimal
policy is relatively straightforward to produce, socially optimal policy often
requires a more detailed examination. In this paper, we identify an issue that
has received far too little attention in welfarist modelling of public policy,
which we name the "hidden assumptions" problem. Hidden assumptions can be
deceptive because they are not expressed explicitly and the social planner
(e.g. a policy maker, a regulator, a legislator) may not give them the critical
attention they need. We argue that ethical expertise has a direct role to play
in public discourse because it is hard to adopt a position on major issues like
public health policy or healthcare prioritisation without making contentious
assumptions about population ethics. We then postulate that ethicists are best
situated to critically evaluate these hidden assumptions, and can therefore
play a vital role in public policy debates.
