Example. John the doctor prescribes large doses of opioids even though he knows this is probably harmful. He reasons, "If I don't do it, my patients will just go to some other doctor who'll do it anyway. Hence, what I'm doing isn't immoral."
Is there a name for the above argument? And have there been any serious analyses of this argument by philosophers (as to whether or not or to what extent it is valid)?
Bernard Williams wrote about this kind of issue. For example, in his contribution to Utilitarianism: For and Against (with JCC Smart, Cambridge University Press, 1973), "Utilitarianism and Moral Self-Indulgence", in Moral Luck (Cambridge University Press, 1981) and in Ethics and the Limits of Philosophy (Harvard University Press, 1985). There is a short account of some of his views in this article.
Part of what is at issue here is whether a person is morally responsible for the outcome of the moral decisions of other people, even if those decisions and outcomes are foreseeable. Suppose I sell weapons knowing that some of them may be used to do bad things, but I know that if I don't sell the weapons then someone else will, so the end result is no worse. In fact, the end result is better if I do it, because I donate 10% of my profits to charity, which is more than my competitors do. On some kinds of consequentialism, I am allowed to take into account the acts of other people when calculating the consequences of my actions, so my activity is justified. By contrast, on a version of absolutism, although I may calculate the foreseeable consequences of my actions, the chain of calculation (for me) ends at the point where another person's moral decision begins. I am responsible for my decision to sell weapons, but I am not responsible if someone else decides to do so, so I cannot justify my bad actions by appeal to what others may do.
As with many issues in ethics, things are a lot more complex than this and there are many variations on both positions.
This is also related to literature on assigning responsibility. For example, this paper contains the following closely related example:
For example, suppose that Suzy throws a rock at a bottle, and shatters it. Billy is waiting in the wings with his rock; if Suzy hadn’t thrown her rock, then Billy would have thrown his, and shattered the bottle.
One can also consider cases where in fact someone else did do it too. Suppose the patient in your example sent a request for a prescription to two doctors at the same time, to maximize his chances, and they both agreed and sent him a prescription. (He will only fill one of the prescriptions.) Even the fact that someone else in fact did give a prescription, and so the additional prescription makes no difference, does not seem to absolve either doctor from responsibility. To make this clear, imagine that he had actually requested the prescription from 100 doctors, but only 2 said yes. One might try to allocate shares of the responsibility to the doctors (e.g., each doctor is half responsible), for example using the Shapley value.
So far as I am aware, Jonathan Glover has coined the name "argument from no difference" for this type of argument in [Glover and Scott-Taggart 1975].
However, apart from the ethical context, there have been similar arguments around in medieval metaphysics and philosophy of science as well. Perhaps, they all should be systematised into one definite fallacy (argumentum ex non differentia?) that would lay down the core idea.
See: Jonathan Glover and Martin J. Scott-Taggart. "It Makes no Difference Whether or Not I Do It," Proceedings of the Aristotelian Society, Supplementary Volumes 49, 1975, pp. 171-209 (in two sections).
It is sometimes called "The Drug Dealer's Defense". It is also related to "The Tragedy of the Commons".
