[Non-Sequitur]

But mere legislation alone could not have ended slavery nationwide. You could have placed limitations on repurchase of slaves, which would not have stood up in court. You could put limits on the length of the program but that would not have meant the end of slavery. Long and short of it is that it would, and did, take was an amendment and nothing you have said indicates that it would have been successful in the face of opposition from the slave states.

[4CJ]

With the courts ruling that slaves were "property" the legislature could effect change via the Commerce clause by simply majority preventing further sale, and Amendment V provided that "private property" could be taken by the government with just compensation.

As a further inducement, emancipation would negate the 3/5ths clause, thereby increasing representation of southern states, certainly something that they would have desired.