Those troops were coming out of the Great Depression. The opportunity to do some truly worthwhile increased the courage and drive to succeed.
IMHO That may be the initial/macro reason to sign up/drafted, etc. In the end, it's the guy next to you that helps generate the courage and the drive to succeed, i.e. surviving. Some sacrifice themselves for their "friends". For the most part, I suspect the guys comin' out of the Higgins or in the Ardennes were thinkin' about themselves and their buddies. They were interested in defeating that enemy soldier/unit and not defeating the Third Reich per se. I hesitate to bring this up on the internet because I don't want this taken as a troll point or an attempt to counter your point. It's just my opinion on a subject that's probably been talked about in every war.