Whataboutism (as in "what about…?") is the practice of responding to an assertion by raising a point or question that expresses a counter-example, which appears to delegitimize the initial assertion. Some examples:

“China has a terrible human rights record.” … “The U.S. is not much better. Look at what we did to the Indians.”

“The Palestinians must be given back their land!” …“What about the millions of war refugees from other countries? The UN doesn’t tell them they have the “right” to reclaim their original homes. Why should the Palestinians be different?”

“The Israeli occupation is illegitimate” … “[That’s] nonsense, there are plenty of big countries that occupied and replaced populations and no one talks about them.” (attributed to Israeli Prime Minister Benjamin Netanyahu).

“Something must be done about police violence!” … “What about violence against the police?”

“Nuclear energy plants are just too expensive to build.” …”What about the potential costs of foregoing nuclear energy?”

What’s wrong with whataboutism? It seems the problem lies with intent:

The communication intent here is often to distract from the content of a topic (red herring). The goal may also be to question the justification for criticism, the legitimacy, integrity, and fairness of the critic, which can take on the character of discrediting the criticism, which may or may not be justified. Common accusations include double standards, and hypocrisy…Whataboutism can also be used to relativize criticism of one's own viewpoints or behaviors. (A: "Long-term unemployment often means poverty in Germany." B: "And what about the starving in Africa and Asia?"). Wikipedia ]

But how do we know another’s intent? What appears to be an attempt to simply change the subject may actually be an attempt to improve the quality of a discussion, to add proper context or examine the speaker’s assumptions. Besides, what’s wrong with trying to redirect attention (“distract”) from a topic if one takes issue with how a claim is presented or defended and wants to sort that out first? And what’s wrong with pointing out double standards or hypocrisy? Or with questioning the justifications given for an opinion?

There’s no easy answer to these questions, although I think relevance is an important consideration. How the US treated Indians in past centuries has no bearing on what we think of China’s human rights record today. But when it comes to whether nuclear plants are too expensive to build, we can’t really evaluate that proposition without asking “compared to what?”.