I doubt that any cliché has been used more frequently to undermine ethical reflection than this one: "Who’s to say what’s right or wrong?" No discussion of morality can proceed very far before someone empties his philosophical quiver and unleashes this sophomoric rhetorical challenge.
The unstated implication behind the question is that ethical principles are nothing more than personal tastes. Given this assumption, the declaration that one type of behavior is better than another becomes equivalent to announcing that steak is good and broccoli bad. All ethical judgments are thus reduced to arbitrary acts of imposition. A thing is labeled ‘bad’ only because some high-handed dude has declared that it is.
It is worth noting that no one employs this shopworn challenge in the arena of science-- because within that discipline it is assumed that some answers are closer to the truth than others. Even in history and sociology, most folks would dismiss "Who’s to say" challenges with a sneer. The obvious response is that "evidence" and "coherence" are the standards for deciding whether a proposition is true or false--not the declaration of some disciplinary czar vested with absolute authority to impose his will on less-influential practitioners.
When it comes to ethics, however, all these considerations are ignored --as if everyone knows that no such thing as ethical evidence exists. Such an idea would come as a shock to Plato, Aristotle, and Aquinas--as well as to more recent thinkers like Kant or John Stuart Mill. Heck, even Karl Marx spent decades cooking his economic books in order to convince readers that Communism was both morally superior and historically inevitable.
In addition to ignoring the possibility that ethical evidence exists, those who fling the "Who’s to say" ratchet into the cogs of ethical reflection also ignore something else--namely, that their rhetorical challenge presupposes the existence of a moral standard that it simultaneously denies.
The "Who’s to say" argument is only effective because it makes any possible answer to the question morally indefensible--since nothing is true simply because so and so says it is. But if nothing can be declared immoral, then there is no basis for rejecting the arbitrary imposition of one person’s values on another. Put succinctly, the "Who’s to say" argument presupposes two contradictory ideas: 1) All moral statements are arbitrary impositions. 2) Arbitrary impositions are immoral.
The clichéd interrogative requires the very morality it denies. And then it employs that sliver of moral indignation to undercut serious moral reflection. The fact that "immoralists" are reduced to blatant self-contradiction in their most popular logical offensive is a bit of evidence worth pondering. The fact that most people don’t recognize this logical con-game is a tribute to the intellectual and moral sloth of a culture that would rather let sleeping consciences lie.