Let me turn that on it’s head.
How about you show me the philosophical turning point that happened prior to the Declaration of Independence and the Federalist Papers to turn our forefathers that you think supported slavery to what they said after 1776.
For context, here’s some of what was written in the Federalist Papers on slavery:
https://vindicatingthefounders.com/library/federalist54.html
Your sentence is badly phrased, but if I can correctly garner from it what you meant to ask, you are asking me what was the turning point?
That's easy. The turning point was 1776 with those five little words Jefferson inserted in the Declaration of independence which got people to thinking that freedom ought to extend to "all men."
For context, here’s some of what was written in the Federalist Papers on slavery:
You need to get more up to speed on the timeline. The Federalist papers all came after the Declaration of Independence. The Federalist papers were created for the purpose of generating support for the adoption of the 1787 constitution, and so they have no bearing on what the Founders were doing in 1776, which was establishing a right to independence.
As I said before in my previous message, you cannot use later actions to justify previous actions. What they did 11 years later has no bearing on what they were doing in 1776.
You can't justify past actions by claiming future actions made your past actions right.