What can we say? The speaker of "War is Kind" is a complicated man. He's clearly a military guy of some sort, one who both commands soldiers on the battlefield (stanzas 2 and 4) and is entrusted with the job of informing people that their loved ones have died (stanzas 1, 3, and 5).
In general, the speaker seems critical of war, but like we said—it's complicated. When he tells his respective addressees not to weep because war is kind, he's definitely being ironic. War, he implies, is not kind at all; it is the reason why the maiden's lover died, why the babe's father died, and why the mother must stare at the body of her dead son.
Even when our speaker's on the battlefield, as seems to be case in stanzas 2 and 4, the speaker seems genuinely disillusioned with the whole warfare deal. The whole idea of the flag is "unexplained" (9), meaning it makes no sense to fight for it; and the battle-god's empire is, ironically, just a field of a thousand corpses. Yowza.
At the same time, the speaker is still plagued by a host of military clichés, still a part of the whole army system. Consider all that stuff in stanzas 2 and 4 about how soldiers are born to drill and die, or the comments in the stanza four about the excellence and virtues of killing. These are the kinds of ideas that start wars in the first place, or prolong them; even though the speaker makes them seem hollow by putting them next to some gruesome battle-field depictions, those ideas are still a part of his identity.
In general, then, the speaker seems like a gruff fellow with a sharp tongue, a realist with a knack for grim details (guys taking their last breath, dying in dirty yellow trenches, etc.), and a master of savage, brutal irony.