> assumes a rational actor model which doesn't model what people actually do
Sure, but in the case of drug prices in countries with national health systems we don't really have any reason to think that the model doesn't reflect reality.
> the deadweight loss in your evaluation can instead be interpreted
Yes, this is exactly my point! The science of economics makes no judgement about the relative moral values at play here. That may very well be a tradeoff people want to make. Or it might not. Economics doesn't comment on that question one way or another, it nearly provides data on the practical outcome of the decision.
Or if you want to use the model, the deadweight loss in your evaluation can instead be interpreted as the price that people are willing to pay for the good feelings of knowing that everyone in the country has accessible and affordable basic health care.