What are some words with negative connotations found in "Dulce Et Decorum Est", and how do they help to instill the poem's overall theme?

Words with a negative connotation in the poem are:
beggars, knock-kneed, coughing, hags, sludge, haunting, trudge, limped, blod-shod,
drunk, fatigue - and those are just in the first stanza of the poem by Wilfred Owen. 
Owen's poem shows the contradiction of the title which means, in essence,  it is sweet
and meet that one should die for one's country.  While the title indicates that there is
great honor in giving up one's life to fight for one's country, the poem itself shows
the gritty reality of war - the exhaustion, the dirt, the blood, the suffering endured. 
The poem describes in grim detail a gas attack and its effects.  By using the words with
negative connotations, Owen makes the harshness of war clear.  He uses words like
clumsy, drowning, helpless, smothering, obscene, cancer, bitter, and desperate because
these present a more vivid picture to the reader.