How do both Hamlet and Don Quixote act as soldiers? What does that tell us about heroism?

Both Hamlet and Don Quixote are used to critique "heroism" that relies too heavily on violence.

Hamlet is pointedly a scholar, not a soldier, despite being the son of a king. When confronted with the warrior's honor code that insists he murder his uncle to avenge his father's death, Hamlet hesitates. While many have seen this as a character flaw of Hamlet's, critics such as Rene Girard in his essay "Hamlet's Dull Revenge" understand Shakespeare to be critiquing an ethic that creates a continuous cycle of bloodshed and revenge.

Hamlet is a sympathetic character, deeply anguished about doing the right thing, to the point of contemplating suicide as a release from his dilemma, but he is no warrior. Thinking, not fighting, is his chief weapon, and he does nothing to prevent Fortinbras from invading his kingdom (arguably, this is his uncle's problem, but as stepson of the king, he might have been created with a more soldierly aspect). By casting this prince as contemplative rather than a warrior and having him raise questions about life and death, Shakespeare critiques unthinking violence and revenge. Laertes' more unreflective and bloodthirsty approach to vengeance, in contrast, is exploited by Claudius for his own purposes, and we are meant to mourn, not celebrate, the pile-up of dead bodies at the play's end. 

Likewise, Don Quixote functions as a critique of heroism. Don Quixote has gone "mad" (this early novel questions madness and sanity) from reading chivalric romances and believes he is a knight errant. He sallies forth to right wrongs, but instead causes nothing but trouble with his would-be heroism, and often, comic book style, ends up brutally beaten before springing back to life and moving onward. He intervenes with a farmer who is beating a worker, only causing a more violent beating and trouble for the worker after he leaves, and he tilts at windmills, thinking they are giants, only causing pain to himself. In fact, the phrase "tilting at windmills" has come to represent misplaced heroism or idealism, or a misapplied use of force for no good end.