From my University US history class, this is how my professor described how slavery was allowed by the Constitution: the founding fathers were generally against

From my University US history class, this is how my professor described how slavery was allowed by the Constitution: the founding fathers were generally against slavery (at least some of them), but they knew that Americans would never agree to the terms of the Constitution if it included abolishing slavery. From what I understand, the founding fathers decided to just let the system work itself out.