I have to disagree with that.
OK.
The further you get from the moment an event occurs, the less objective you become and the more reliant you become on dates and data.
What I'm talking about is how the assination of President Lincoln immediately elevated him to martyr status and if anyone had anything legitimately negative to say about him or his performance as President it was immediately washed away. If you don't believe me, be sure to read Walt Whitman's poem, "O Captain, My Captain." After his assassination Lincoln was practically worshipped and most people could not be objective if they tried.
You can read primary sources and gain some insight, but at some point, as society transforms, you begin to lose conceptual understanding of the psychology of the participants, the results of peer pressure, social pressure, political and religious beliefs, etc. The primary sources only give you a small percentage of participant's perspectives on the events and they may even contradict each other in how they see the end results.
Yes, primary sources are invaluable to historians. But a historian also has to understand the times in which a person or event lived and was shaped. I agree, that gets very difficult. I also understand the competition, peer pressure, and general paranoia that someone will steal ideas from another in the field of professional historians.
Trust me, I do a lot of historical research. And I read the results of others' research. I recently read a series of forum posts between two guys who are noted historians on Confederate uniforms, both having over 20 years experience as professional historians and having published books on the topic, and they couldn't have disagreed more about whether or not civilian pattern sack coats were common in the Army of Northern Virginia in 1862-63 or not. Same data, same resources, different conclusions. It is a minor topic and there are tons of military records and images to support both positions, it just comes down to how you interpret the information.
You've just made my case that you cannot say with certainty that your positions on Abraham Lincoln's views on American Slavery and race are ironclad, MJ. You can see that, can't you?
Interesting discussion. My daughter recently got her masters degree in history and she has enlighted me a great deal on the world of "professional historians." I must say, as a result, I look at many things differently now.