When Conditional Reasons Don't Collapse: Regime Sensitivity and Prioritarianism

In path-dependent policy settings, ethical reasoning often proceeds regime by regime: compare policies conditional on lock-in versus flexibility (or fragility versus robustness), then aggregate. We identify a structural failure of that move under terminal ex ante prioritarianism: when policies endogenously shift regime probabilities, within-regime improvements need not aggregate to an overall improvement. The key normative issue is not heuristic use of scenarios, but justificatory standing: whether regime-conditioned claims may function as defeater-capable reasons in public justification. Given admissible stable downstream macrostates and a weak route-neutral conditional-dominance norm, terminal prioritarianism faces a trilemma: deny such standing, restrict admissible regimes to near relabelings of terminal outcomes, or incorporate trajectory-sensitive structure and abandon endpoint-collapsibility in substance. The diagnosis is moderate, extends to endpoint-aggregative terminal outcome-lottery views more generally, and motivates constructive repair conditions under which the dominance constraint can be recovered.