Honor runs throughout the other themes of "If We Must Die," and it is the underlying idea of the poem. The speaker feels that on his side are the "good guys," because they are honorable men and will only fight honorably. The fact is, they are not fighting for survival; they already know they will die. They will fight honorably so that their death will not be meaningless, and so that, maybe, their enemy will honor them in death.
The speaker values many things as honorable, including revenge, some forms of death, unshakable bravery, and fighting by the rules when others don't. The speaker's reliance on honor to provide his life with meaning leaves him no other option that to give up his life.