Our grandparents likely knew nothing of why they went to war, or the global politics at the time, or that the Daily Mail and King Edward XIII supported Hitler. They were very ignorant of the world compared with people today (education-wise). The Americans didn't get involved until 1942 (the war started in 1939). No one had any idea about the concentration camps and gas chambers until they found them.
Looking at the war with rose-tinted glasses does not help anyone.