The practical reality is that nobody today can develop a sufficient depth of knowledge in more than a couple of niche subjects at best to be "right" about them at anything other than the most superficial of levels.
Somebody might read a book, or several books, or several books and some blogs about a subject, or even take one or several courses in it, but that doesn't mean they know it. They know some things about it, and some of the things they think they know about it will be wrong.
Maybe part of the disagreement here that isn't being addressed is the difference between ideas (or facts) and principles. My principles have changed very little over the years, and so the direction of my ideas haven't either. But my ideas change frequently because there are only a few subjects about which I know anything and I am a moron in the rest.
edit: and even in those couple of subjects where I might claim some expertise, I'm wrong frustratingly often.