I always think of this little poem from Rudyard Kipling.
Going into WWI, Kipling was a hugely pro-war idiot. That was until his son was killed at the Battle of Loos—the kid was only 18—and RK realized how wrong he was. I think that makes this little poem that much more devastating.
From Kipling’s Epitaphs (1914-1918):
If any question why we died,
Tell them—because our fathers lied.