It's simple. If I think like the enemy, I will not only be able to defend against him, but ultimately defeat him.
Very few people have ever requested I "think like a terrorist," but that's what makes anti-terrorism training so valuable.
It also makes a lot of sense, but so often we get caught up in our own problems and lives, we forget an attack can happen anytime, anywhere. As uniformed personnel or civilian employees, we all work for the United States military, which inherently puts us at risk for dissent, anti-U.S. sentiment or possibly even violence.