I think you're thinking of the one about the abolitionists from the 1850s, which I've been looking for, myself. The Hitler one said

"Several reliable, well-informed sources confirmed the idea that Hitler's anti-Semitism was not so genuine or violent as it sounded, and that he was merely using anti-Semitic propaganda as a bait to catch masses of followers and keep them aroused, enthusiastic, and in line for the time when his organization is perfected and sufficiently powerful to be employed effectively for political purposes."

and

"You can't expect the masses to understand or appreciate your finer real aims," the newspaper quoted the politician as saying. "You must feed the masses with cruder morsels and ideas like anti-Semitism. It would be politically all wrong to tell them the truth about where you really are leading them."

The NYT's own account of its embarrassing early Hitler articles: https://archive.nytimes.com/www.nytimes.com/times-insider/2015/02/10/1922-hitler-in-bavaria

(Article about it, with easier-to-copy quotations)

Edit - Aha! Found the abolitionist one. https://nitter.net/danielradosh/status/1461346660185825288

Edit edit - And a Citations Needed episode where they discuss it: https://citationsneeded.medium.com/episode-127-democratic-leaderships-predictable-scapegoating-of-defund-the-police-75ef49af193a

“The very best thing that could possibly be done towards the abolition of Slavery would be for the North to stop talking about it.”

“Ten years of absolute silence would do more than fifty of turmoil and hostility, towards a peaceful removal of the evil. It is quite possible that the Abolition crusade may force a bloody and violent termination of the system, but this no sane man desires: and any other solution of the problem is infinitely [slowed] by the incessant intermeddling of parties who have neither responsibility nor power in regard to the subject. The great necessity is to let the South alone, — to leave them leisure to think of their own affairs, — to throw upon them the necessity of studying their own condition and of looking into their own future. So long as we engross their thoughts by alarming their fears, they have neither time nor inclination to examine the question except from this single point of view.

“Emancipation, whenever it comes, must be the work of the Slave States themselves. They must adopt it from a conviction of its necessity to their own well-being.”