Many people approach political questions as a war to defend their ideological turf. Others are policy wonks who want to turn everything into a debate about contemporary policies. (How boring.) Some people mean well but don't understand what the words "all things equal" mean. This can prevent them from having honest, interesting, or relevant dialogue. It can prevent them from being able to do philosophy at even an introductory undergraduate level.
You might want to discuss abstract principles with such people, but they can’t help but assume you’re trying to push a party line, even if they don’t know or have misidentified what that party line is.
So, for instance, you pose a hypothetical—“Imagine a situation in which these are the facts, and the facts forced us to choose between A and B…”—and rather than going along with the thought experiment, such people attack. “But Sweden isn’t like that!” Who said it was? “But those aren’t the facts!” Who said they were? “Wouldn’t this alternative scenario be more realistic?” It may well be. So what?
Thought experiments are artificial––and often highly unrealistic––on purpose. Complaining that a thought experiment is unrealistic is a bit like complaining to a puppet-maker that his puppets aren’t real people. Until the puppet-maker exhibits signs of mental illness, it’s a bit presumptuous to remind him Pinocchio is not a real boy. Scientific experiments create artificial environments in order to test the impact of one factor while controlling for others. Thought experiments do the same. They help us test principles.
Consider “brain in the vat” thought experiments. A philosopher might say, “It’s logically possible that you are a brain in a vat. If you were, you’d be unable to discern otherwise, and your experiences of the external world would be non-veridical. Given that you can’t demonstrate that you are not a brain in a vat, do you right now have knowledge of the external world?” If someone responds, “But given our current level of technology, we actually cannot create brain in the vat scenarios, you moron,” the philosopher just has to shake his head. When did he say we could create brain the vat scenarios?
If somebody asks, “If X were true, what would follow?,” it’s not relevant to argue that X is false. For instance, I think homosexuality is morally neutral, just as heterosexuality is morally neutral. I deny that homosexuality is inherently self-destructive, degrading, or harmful, as some religious people claim. However, suppose someone asked me, “Imagine it turned out that homosexuality were inherently self-destructive and that homosexuals could not flourish. Would it then be acceptable for governments to outlaw homosexuality?” I wouldn’t respond by arguing that homosexuality is not harmful. That would be pretty dense on my part. Instead, I would understand the person to be asking me about issues in paternalism and personal liberty.
So, back to the ParetoSuperiorLand and Fairnessland thought experiment. It might turn out fortuitously that serving the interests of the poor today and serving the interests of the poor tomorrow require that same actions from us. I sure hope so. I love it when all the things I care about come together. Or, it might turn out unfortunately that these goals come apart, and we are forced to choose. If we are forced to choose, we'll need to have some principles to help us decide.