He lived at a time when the people around him were risking their careers and sometimes their lives to enlist during a war. He didn’t.
Director John Ford famously harrassed him for that decision during the filming of a movie.
I’m not blaming him for that decision but IMO a great American it does not make.
So, by your logic every man/woman actor that did not enlist and fight on the front lines was not a great American? Some that did saw combat and performed admirably others made films while in the military, are they not great?
A great many of them that did not enlist made films, entertained troops on leave, and sold war bonds. That did a lot for morale and war finance.