There is a clear affinity that Tennyson displays for the soldiers in "The Charge of the Light Brigade." Taken from the newspaper reporting of the Battle of Balaclava in the Crimean War, in which British forces died, Tennyson wants to construct a homage to their sacrifice. This is where the poem's purpose emerges. There is an extolling of the loyalty of the forces. A set of lines from the poem's second stanza confirms this:
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die:
Into the valley of Death
The poem brings out the heroism of the soldiers. Why they died is understood: Loyalty to country. Tennyson's poem's purpose is to bring out the honor in the soldiers' sacrifice. It is meant to raise consciousness of how certain death was for the soldiers and how little fear they displayed in confronting it. The poem's purpose is not to double guess the cruelty of war. Rather, it is meant to value the individuals who willingly sacrifice for it.
The single most important line in the poem is "someone had blundered." It is a commentary on strategic and bureaucratic incompetence not merely a simple-minded glorification of soldiers.