Bierce chooses a Southern protagonist to prevent readers from arriving at snap judgments about him. The story was written in 1890, twenty five years after the end of the American Civil War. It is likely that anyone reading the story at that time would have strong feelings about the war and its outcome. Because Peyton Farquhar is a Southerner and "a well-to-do planter," a slave owner "devoted to the Southern cause," he might be viewed as a villain by many readers.
However, on some level, readers are encouraged to respect his dedication to his cause: although he did not join the army, he wanted to contribute in a meaningful way to the war effort, and this motivated his decision to attempt to burn down the Owl Creek Bridge. He was "a civilian who was at heart a soldier," something most people would likely respect; though he "without too much qualification assented to at least part of the frankly villainous dictum that all is fair in love and war." He is, in many ways, someone to be respected for his dedication to his principles, but, at the same time, he is somewhat savage in his adherence to such a barbaric adage.
We cannot simply write Farquhar off as either a hero or a villain, and this adds depth to the character and the story.