So -- Yes, virtually any element of US history is problematic. So is every concept from every culture/nation that came before it.
And even if we recede to this newspeak version of "problematic" as meaning "immoral" (in one way or another)... it's a completely facile exercise to see that every human society has struggled and/or been oppressed throughout history. So the unerring tendency for the current wave of critical postmodern-inspired social rhetoric to focus on one set of targets rings extremely hollow. "US History is problematic" (and awful and deeply shameful and requires this raft of policy prescriptions I like, etc)... but god forbid you try to discuss extant social structures or historical conflicts in Africa.
Just an internet stranger's opinion, but I also think it might be worth engaging with some of these ideas a little more before writing them off, since it sounds like you share a position I once had - annoyed by 'problematic' stuff everywhere, for instance - and furthermore share an apparent misunderstanding of postmodernism with the Jordan Peterson crowd. But you can take a critical eye to the power structures and ways of thinking of the past, and their implications for our social structures today, without screeching or hysteria. At least be open to it :)
One man's deflection is another man's context.
I think the answer is pretty simple, actually: there is demand for writing that attacks the reader, and validates the reader's feelings of self-loathing. Ultimately its a form of narcissism, but of the negative sort. "I am the root of all the problems of the world," the reader wishes to be convinced of this, and given arguments to make the connection. It is a dangerous sort of narcissism too because its explicitly cloaked in the guise of compassion and guilt and shame. "Virtue signaling" is a part of it, but I think it goes much deeper, and is absurd in a way that few commentators have touched - except, maybe, for the latter seasons of South Park.
It's a pity because there are good things to analyze and do at the systemic level to make life better for everyone. Particularly at the physical structural level, like designing cities for people and not cars, for sustainability and not financier profits. And there are good things to do at the personal level, like help a stranger in need, or recognize the real pain a thoughtless word may cause. But, because of the cognitive distortions that come with narcissism, these are also distorted, misused, and weaponized into a powerful tool of passive aggression.
Perhaps a simple approach would be to challenge such people to do 10 things for every 1 thing they say.
Commit enough fouls in a basketball game and they aren't supposed to stop calling fouls on you because it's tedious to blow the whistle every time! ... though... there are teams that have employed exactly this strategy, so maybe it's an even better metaphor than it seems on the face of it!
If you want to say we should start over and start a new game - maybe reset all the property and wealth in the country - sure, then maybe we would have less reason to talk about the current one.
Because there's a big difference between "I find this tiring that people keep talking about it, we already know" - in which case we should be talking about what we can do, instead - and "I disagree with these claims, but instead of trying to disprove them, I'm going to try to discredit them by complaining that I've heard it before."
It sounds like the latter - questions like "how far back do things need to be" sounds like a disagreement that the effects continue. In which case: be straightforward! Just come out and disagree directly! Because the answer to a question like that is obviously situational, and depends on how much impact the sin had and continues to have.
I would have hoped "before I was born" to be far enough back, but evidently it isn't.
[1] https://en.m.wikipedia.org/wiki/The_New_York_Times_Best_Sell...
We can finally let Thomas Nagel know what it is like to be a bat.
"At least a hundred million inquiring minds have read “Everything You Always Wanted to Know About Sex."
But my reading is still that it's probably a much more non-malicious wordplay connection to the the "but were afraid to ask" part of the book's title.