Whataboutism---The charge is meant to censor the speaker, excuse U.S. actions, and defend its human rights violations. The denials and apologies are exactly why whataboutism should be defended. It is terrible when lies and crimes are not countered with verifiable information exposing them.
The term has gained popularity in part because there is so much hypocrisy to point out and there are so many adherents to American exceptionalism who defend what they should condemn.
If Vladimir Putin is described as a war criminal, thug, dictator, and a modern day Hitler, it is appropriate and indeed necessary to ask about American presidents. For brevity’s sake consider only those American presidents who served since 2001. U.S. invasions and interventions in western Asia, North Africa, central Asia and the Horn of Africa have displaced more than 37 million people since the “war on terror” began. Why shouldn’t George W. Bush, Barack Obama, Donald Trump and Joe Biden be called war criminals too? Silence in the face of their criminality gives license and approval to U.S. aggressions.
People who claim whataboutism just want to invalidate any arguments against theirs. It's like calling someone a conspiracy theorist. "Whataboutism" shows hypocrisy and then that person claiming whataboutism would have to defend that claim as well and it would go against their core beliefs of supporting a person like Biden or Obama or their side like the Republicans or Democrats.
The problem with whataboutism is that even if your reply criticisms are accurate, often times the conclusion the whataboutism user proposes or seems to propose doesn't follow logically. e.g.
A: Putin shouldn't be invading a sovereign nation under false pretenses.
B: What about Biden? He did/supported the same type of action.
So even if B is correct, it doesn't change the fact that A is correct. Whataboutism isn't a counterargument, it's basically just tattling. While it could be important for a larger debate, it's not constructive to the discussion at hand. No one is excusing anything. Just because the US was wrong, doesn't mean we should collectively be fine with everyone continuing to behave poorly. Do you really not see how that is a self-defeating proposition? If you could ever point to anyone doing something wrong, you could never again in the history of mankind call out another for the same wrong behavior. Wasn't it you that made such a claim a few days ago?? The most recent example you could give of the United States conquering land was 177 years ago and you STILL used a whataboutism justification for Putin. That is laughably idiotic.