Dean and Sam visit a bar filled with off-duty Air Force personnel on November eleventh and raise a toast to their friends who fell in this Godforsaken holy war; they mean Mary and John, Jo and Ellen, but everyone hears Carrasco and Espinoza, Andersen and Helton, everyone who's died in the past decade while wearing a United States uniform. If it's this hard to tell what's a sign of the apocalypse and what's people being (flawed, murderous, destructive) people, if humans will go right on killing each other even without demons and angels egging them on... Dean can't bear the thought of the disappointment in John's and Ellen's eyes if he gives up, and Sam flatly refuses to prove Lucifer right; some days that's all that keeps them from giving up.
[Note: Carrasco et al are, according to cnn dot com, the four most recent (as of Nov 11 2009) American casualties of enemy action in Iraq.]