Billy Budd may be easier to understand when taking a look at what was happening in Europe at the time this story takes place.
The year is 1797. The French are in the throes of the French Revolutionary War, and in 1797, England is attempting to thwart the French's plan to "join a large Spanish fleet."
As was the custom of the English, especially during times of war, when sailors were needed, the Press gangs would actually impress (kidnap/take by force) men into service for the Royal Navy. (This was a legally sanctioned action that had been in existence for many years in England.) Those impressed included mostly Englishmen, of the seafaring sort, who were between eighteen and forty-five years of age. They were basically prisoners of the Royal Navy.
This situation affects the men on the ship called Rights-of-Man. Billy Budd is one of the sailors on the ship who has been impressed into service. It is logical to assume that he and others are treated poorly. They were generally taken into service on the spot, without time to even communicate with family members.
The frustration and resentment of being pressed sailors would not have endeared the senior crew members of ship to the sailors who were not their by their own choice.
And because of what was going on with the French at the time, rebellion was in the air. People who had been repressed for so long were now uniting and fighting back at their oppressors. They were planning ways to overthrow the upper classes who wielded the power and controlled the money in France, and bring a revolution for change to the forefront of social reform. This battle moved out across Europe as the French made war on other countries.
These sentiments would have been clearly understood by those impressed on the same ship with Billy Budd.
The senior officers perceive the threat of a mutiny on board; when accused, Billy Budd stabs his accuser. He is ultimately hanged for doing so. However, the same frustration the French feel is what all oppressed people experience: rage, fear, and frustration.
This historical events/practices allow the reader to be more empathetic to Billy Budd's actions: while murdering is wrong, impressment denies the rights of those taken. I am sure this was not the only incident of the times, where people were motivated for the same reasons.