To set the context: After a nighttime engagement with the enemy "Huns," the speaker's company is shelled with poison gas as it withdraws. One soldier, deafened by gunfire perhaps, doesn't hear the alarm, "Gas! GAS! Quick boys!" and didn't get his mask on in time--"But someone still was yelling out and stumbling / And flound'ring like a man in fire or lime ..." Here is the aftermath of that "helpless sight"--
Owen was no coward: he was actually "blown up" by an exploding shell--the death du jour in Iraq or Afghanistan--but after treatment for concussion and shell-shock, he was returned to the front, won the Military Cross for heroism in action (Audie-Murphy style: he killed a bunch of Germans with their captured machine gun!), and wrote his poetry ... only to be shot and killed in the last week of the war. His beloved mother received the news as the Armistice bells were ringing.
If in some smothering dreams' you too could pace
Behind the wagon that we flung him in,
And watch the white eyes writhing in his face,
His hanging face, like a devil's sick of sin,
If you could hear at every jolt, the blood
Come gargling from the froth-corrupted lungs
Bitter as the cud
Of vile, incurable sores on innocent tongues,--
My friend, you would not tell with such high zest
To children ardent for some desperate glory,
The old Lie: Dulce et decorum est
Pro patria mori.
The poet's point is that in modern warfare there is nothing "sweet and decorous" anymore about dying for one's country (though the Horatian line is still the motto of England's famed Sandhurst Academy). No mano a mano flashing of swords and genteel swashing of buckles on this battlefield. No, much to his mortification (in every sense), Owen finds the war a craven subhuman slaughterhouse, where ignorant armies clash by night, and where a once-gallant soldier can be "flung" onto the ignominy of a meat-wagon.
Nonetheless, Wilfred Owen fought on to the end ... because for him at least (1) there was a clearly defined "enemy"; (2) his homeland across the the channel was already threatened by German submarines, blockades, and future invasion; and (3) the French allies were not such a bad lot to be fighting for. Now, the Middle East is no less a craven blood-bath than Owen's WWI France--our soldiers are literally "floun'dring ... in fire and lime"--but where are those casus belli for keeping our soldiers at war, or for them to keep fighting? Take the Blogman's quiz: go back to nos. 1, 2, and 3 above and try to apply them to AfghanIraqiStan. Give up?