Very good post. Two observations -

1. Most people's beliefs aren't based on evidence. Some of their evidence being discredited or looking less strong usually won't cause them to revise their beliefs.

2. This is partially because people's beliefs are a lot more binary than the real world is. The guy might think that admitting a Scotsman committed a crime would be switching from "All Scotsmen are the best" to "All Scotsmen are not the best," which would be hard for him if he's proud of his heritage.

In reality, he could say something like, "I was mistaken - Scots aren't perfect. We're still great people, though" - but most people think that admitting one crack into the armor will break the whole thing, so they fight it.