In teaching ethics, and in paying too much attention to politics, I encounter the sentiment that "We've always had [insert great misfortune], so we'll never be without it" over and over again. The sentiment is offered as a reason not to work toward alleviating poverty, warfare, disease, and all manner of problems that simply affect the whole globe and likely look to big to overcome. Still, I think this is a problematic line of reasoning, and one that we should stamp out as if it were a logical fallacy (and might trade on one, more below).
Ok, so why is it a problem? For one, it's simply conversation-stopping in any ethical debate. Should we devote resources to researching Sudden Infant Death Syndrome? Well, babies have always died for no reason, so we'll never prevent that...There is simply nothing to do but throw one's hands in the air and give up.
Now, in ethics, there is some reason to take this argument seriously. There is a very general principle that guides normative theory: Ought implies can. We cannot demand that people do the impossible, so morality can never require that we act in some way beyond our capabilities. We work toward the good insofar as we are able.
On the other hand, the argument also trades on the Naturalistic Fallacy: you can't derive a normative statement from a descriptive one. Women were treated as property for centuries, and in some places still are, but that doesn't make it right. People murder each other every day, but we still put murders in prison. Morality does not describe the world as we find it; it describes the world as we should leave it.
Now that we see how the sentiment has some intuitive appeal, and a sense of why we should be suspect of it, how should we respond to these assertions? What should we get our students (and our peers) to think about when they say "But this is just how it is"?
For me, the most important thing to grasp is this: true moral evils stem from the decisions of human beings. We live in a causal world, and the things we see around us are effects of existing causes and conditions. There is, as it were, nothing that "just is" any particular way. There is always something that sustains a particular state of affairs. As such, there is no prevailing condition in the world that is truly necessary, only the contingent result of contingent circumstance.
Contingency is a powerful concept. It strips our world of intrinsic, given meaning. It also forces us to understand ourselves as both agents and patients of causation. We are affected, but we also affect. Even if the causes of world hunger or distributive justice are systemic and institutional (and some are), by surrendering to this contingent state, we implicitly endorse all of the causes and conditions that create that state. We validate the unfairness that prevents food from reaching the people who need it, that confines medication to the boundaries of patent law and wealthy patients, that ensures that some people have to work much harder to achieve an economic status that others reach through failure.
Our task is to make the world fair, to correct these injustices and leave the world better off than we found it. Causation is both blind and brutal. We can be likewise cold and accepting, or we can choose the harder path and create kindness and compassion. The choice of what we accept is ours, and the remaining question is how to do it, not whether we should.