All of them, rather than compromise their biography of Taney. Roger Taney was the subject of their work. Deliberately leaving out an important part of his life and career would cast doubt on the rest of their research.
I realize that accuracy is unimportant to you if it gets in the way of your agenda. But you aren't a professional historian and biographer. Accuracy for them is the life's blood of their work. It forms the foundation for their professional reputations. To you it is nothing, to them it is everything. And the shame is that you will never, ever understand that.
I do not believe that. I believe there has been a deliberate propaganda war against the South since before the Civil War even began, and the "group think" of the North East prevents them from even looking at things in an objective manner. If you grow up in that environment, you will simply dismiss anything that does not conform to what you have been told to believe for all of your life.