Remember Lieutenant Dan in Forrest Gump? He's from a later war, but we're betting that his tone is pretty much the voice in your head when you read "Dulce et Decorum Est." Before he gets on the shrimp boat with Forrest, he's a bitter and broken man. He just can't figure out how the world could deal him this hand of cards, or why no one, not even his best friends, can seem to understand the horror that he's experienced.
That bitterness tracks well into this poem, which savagely attacks those back home who incite innocent young boys to fight impossible and unending battles. As far as our speaker is concerned, a few lines of poetry aren't going to compensate for the fact that your friend has been killed, or that he continues to haunt your nightmares.
Like Wilfred Owen, our speaker is up on his Latin poetry. Strangely enough, reciting sections of Horace's Odes wasn't all that uncommon for the people during the war. Many people went to public school. (For folks in England, "public" school actually means private school. We're not really sure why.) Everyone who went to public school learned the same Latin poems and heard the same speeches about glory and honor. Because our speaker knows that his readers are the educated elite, he's got no problem tossing off quotes from Horace.
The speaker of this poem is also a soldier through and through. He's trudging with the sleeping men at the beginning of the poem and he's dreaming about the same men at the poem's end. The center of the poem hinges on our speaker as a witness. As he says, "I saw him drowning" (14). Line 14 is the literal center of the poem. More importantly, it's the thematic heart of the poem, as well. The "drowning" of a man in gas fumes becomes the image that occupies our speaker for the rest of the poem.
In some ways, this scene of the poem is literally the only scene that matters to our speaker now. There's no way for him to move forward. He plays and re-plays the "smothering dreams" of battle in his head (17). Ironically, our speaker lets us see that the "men [who] marched asleep" had things pretty good: sure, their feet were bloody and their bodies torn up, but at least they could sleep in relative peace (5). Our fellow, on the other hand, can't sleep at all. His dreams might even be worse than the battle itself. Death is his constant companion. All that trauma would be enough to make anyone hate the warmongers at home.