Putting aside the issue of "cancellation," by your logic we shouldn't even harshly criticize people for doing things in a given time period if they were widely "accepted." But that is morally and practically absurd on a couple of levels.
First, it would mean that we couldn't even harshly criticize American slavery as an institution and those who practiced it, because it was "accepted" in the society. But that's morally repellent. There are things that are morally wrong even if accepted by those in positions of power and practiced widely. And since enslavement rested on theft (of labor and bodies) and the unjust killing of others as well (millions died during the middle passage, and death was expected on the part of much of the human cargo), it violated ancient moral codes, including but not limited to the Ten Commandments. The fact that elites in the U.S. (and elsewhere) ignored those moral truths and made slavery "acceptable" doesn't mean those who practiced it should escape harsh judgment and condemnation.
Second, your position ignores the issue of WHO accepted certain social norms at given times. And those decisions are always about who has the power to enforce their beliefs.
Marital rape was considered acceptable for a long time (it was actually not considered rape at all) because MEN accepted it and had the power to enshrine their perceptions of right and wrong in law. Women never thought it was OK but didn't have the power to object effectively. Obviously, those men were full of shit. And yes, husbands who raped their wives in the 1930 or the 1980s, for that matter, at which point it was still "acceptable" in certain states, were fucking rapists and should be viewed as such. Forever. Should they be prosecuted? No, because criminal prosecution requires an actual law to be violated. But should we give them a pass, morally? Hell no. They were monsters. No exceptions.
Likewise, slavery was OK to those who ran the system. Needless to say, not to those who were enslaved.
Even the example you mention -- parents beating their kids or spanking them -- was NOT universally accepted even at that time. I'm older than you. My parents always objected to laying hands on kids and indeed most nations do not allow corporal punishment in schools or look nearly so sanguinely on parents doing it either, when compared to the US. It is not something that was "Ok back then." It wasn't, at least according to literally all the child development evidence. It was wrong then, and it's wrong now. Stacey Patton's work on this is definitive and I highly recommend it.
Oh, and as per the power argument earlier, it was obviously never "acceptable" to most kids being hit by parents. Oh sure, folks will say stupid shit like "I got whooped and I turned out OK," but did ya? really? I always think its funny when people who got spanked and worse say how if more kids got whooped today there might be less crime. Sure, because the prisons are just filled by people who were given time outs and redirection by parents. Bullshit, they're filled with people who got spanked and whooped all the time. It's rationalization. All of it.
So while I can agree that "cancellation" of people for retroactive offenses is absurd, the argument you are making more broadly is incredibly dangerous and wrongheaded. There is right and wrong. Morally and practically. And those things shouldn't be determined by who has the power to enforce their norms, whether that's people I agree with or disagree with. They ought to be determined based on some relatively objective (since nothing is perfectly objective) standard of non-coercive, non-abusive, non-oppressive and non-denigrating behavior. We can and will, as reasonable people, perhaps disagree over what that reasonably objective standard should be. Cool. But we cannot afford to act like there isn't one and that it's OK to give our assent to shitty behavior and treatment of others, just because "things were different" (to some people) back then.
