What these brave men did to protect our freedoms is why we should NEVER give up our freedoms.
When I was a child, during a military parade/event in Long Beach (CA), a Marine let me sit behind a 50 cal and then he gave me a can of c-rations. Best day ever.
I don't know the phycology of it, but a brotherhood built on shared adversity is difficult to explain. Veterans, especially combat veterans know and understand this brotherhood. It is deeper and more compassionate than a family bond and it is the driving force for their love of country, fore no one other than they know the true cost to preserve it.