Lol! America was built on a foundation of freedom? They certainly turned that way over time but the initial work, the actual foundation on which the country was built, was the work of the British colonisers. The subjects of the British Empire, who achieved the success they did because people, materials and wealth were provided by a decidedly unfree form of government and society.
Then, they declared their emancipation, insisted that no one had the right to treat them that way and they deserved life, liberty and the pursuit of happiness... And then set about importing other people, who were treated worse than cattle and worked to death, stripped rather starkly of life, liberty and happiness along with everything else.
But don't worry, it was only about a hundred years before they got over that whole thing. I think it's safe to say though that between the English colonial period and the hundred years of slavery, we're well past the point where you can claim America is built on a foundation of liberty!
Dude, you keep saying "they" as if the first colonists who went to North America to find religious freedom, the "Founding Fathers", and the Southern slaverholders were all the same group of individuals. They were not. There was some overlap of course, but not all of what later became the USA had slaves, not at all.
If you were a "good old boy" from the South, and someone raised the matter of how your "peculiar institution" fitted in with the whole Unalienable Human Rights thing, you had some options:
- Deny that those rights applied to Negroes
- Deny that slavery was a violation of those rights
- Deflect the question somehow
- Refuse to debate the matter and simply threaten violence if they bring it up
- All of the above