You may be confused because the article doesn't say what you are saying in your post. In grammar school they used to give tests on what we actually read in a paragraph. It led students to think about what was really written as opposed to what we assumed.

Nowhere in E J Dionne's article does he say that McPherson is "king" or the only expert in the field. I've thought this many times, and said so occasionally, people really should read more carefully.

When we've already made up our minds that "the Civil War had nothing to do with slavery!" and we read something to the contrary, oftentimes we simply reject the statement and anything else that goes with it. That's unfortunate, because it leads to one-sided thinking, and we miss a lot of history that way.

We always told our students, be skeptical - don't be negative. In other words, don't reject a statement out of hand before you have investigated and reviewed its substance.