The murder of Minnie Wright's husband was the consequence of pent up, disturbed and emotional chaos caused by an extended period of domestic violence. Minnie was isolated in the middle of nowhere. She was also isolated from her peers and from the rest of society.
As a result, she was under an incredible amount of mental and psychological stress. When John Wright decided to take his abuse one step further and chooses to kill the only thing that Minnie had left, her canary, Minnie loses the last of her mental faculties. Perhaps she did not want her abuse to be transferred to that which she loved. She then snaps and kills her husband.
Life is not ours to take. Unfortunately, Minnie Wright had nobody to defend her from the monster that her husband had become. All that she had was her canary, her misery, and her loneliness. Grief can play tricks on one's mind and, when extreme grief hits, crazy things can happen.
The women were concerned because they knew that evidence that proved a "snap" would confirm the men's suspicions about Minnie having killed her husband.
Crime is never justifiable. It always leads to chaos and tragedy. It is simply too sad that Minnie had to implode and then explode the way that she did. It could have been preventable, but certainly also avoidable. John Wright has the same right to live as everyone else. That he made his wife's life miserable there is no doubt. Did he ask for what he got? Indirectly, yes. It is not justifiable, but it is expected that a slave will rebel to a master the way the abused goes against the abuser. It is action and reaction, but it is never ever justifiable to take a human life. Or any life, to that effect.