I don't dispute that this is one reason it wasn't done. But it was NOT the legal reasoning.
Lincoln wanted to end slavery. Lost causers want to argue he only wanted to save the Union ("at all costs"). Actually he (and all Republicans) wanted both. And while it is true that they wanted to save the Union more, that fact is too often used to support a claim that Lincoln "didn't want to end slavery," or that the primary cause of the Civil War was not slavery. Neither of those statements is true.
Can we also agree that Obama is a fraud and a fiasco?