What were Wilfred Owen's feelings about the event he witnessed and the effect of war on people's lives?

Although Wilfred Owen, the author of "Dulce et Decorum Est," was an officer who fought in World War I for the British, it is not clear whether the event he describes in the poem is one he personally witnessed. Since poets often write in the voice of a persona, one cannot take a poem as autobiographical unless the poet has provided evidence elsewhere that that is the case. Nevertheless, even if Owen did not experience the exact event described in the poem, he certainly was involved in similar situations. He was hospitalized for shell shock, and while in the hospital he met Siegfried Sassoon, a writer of fiercely realistic war poetry. Sassoon influenced him to process his experiences through poetry. 

Another inspiration for this poem, from the negative side, was Jessie Pope, a writer for periodicals who wrote jingoistic war poetry that tried to entice young men to enlist. Owen originally titled this poem "To Jessie Pope." You can read a sample of the type of poem Owen was reacting to at the link below. 

From the poem we can deduce that Owen was deeply affected by the horrors of World War I, particularly trench and gas warfare. The poem describes nightmares similar to what Owen experienced: "In all my dreams, before my helpless sight, he plunges at me, guttering, choking, drowning." Witnessing a kind of warfare the world had never seen before was emotionally scarring to the men who fought. No wonder Owen was angered by the unrealistic and rosy picture the recruiting efforts painted for young boys. His anger is apparent when he says that if you (that is, Jessie Pope) could suffer from similar nightmares, you would not tell gullible young men the lie that it is sweet and fitting to die for one's country. 

Owen was not against fighting for one's country. After he was released from the hospital, he returned to battle. He even won the award of the Military Cross for his valor. Sadly, he died in action a week before the end of the war. What Owen objected to, strenuously and eloquently, was deceiving young men into enlisting before they really understood what they were getting into. His realistic war poetry helped to raise awareness among potential recruits and the country at large about the sacrifice that Britain required of its soldiers.