It's not Dunning-Kruger, it's because engineers have a very black-and-white view of the world. When they're engineering something, either it works according to specs or it doesn't. Also, engineers tend to be more religious and conservative for some reason; this is very different from scientists who are the opposite. I think this all works together somehow to make engineers more prone to extremism, to try to force the world to act the way they think it should.