Final answer:
Martha and Abby are likely characters from the play 'Arsenic and Old Lace', where they kill elderly bachelors as a form of mercy killing, believing they're helping these men escape loneliness.
Step-by-step explanation:
The question "Why are Martha and Abby killing men?" appears to refer to characters from a work of fiction, likely a play or a novel. Without additional context, it's not possible to provide a specific reason for their actions. However, if the characters are from the well-known play Arsenic and Old Lace by Joseph Kesselring, Martha and Abby Brewster kill men as a form of mercy killing. They believe they're helping lonely elderly bachelors by poisoning them with arsenic-laced wine, thus putting them out of their perceived misery. This act is wrapped in a dark comedic tone throughout the play and serves as a satirical commentary on the nature of charity and the perception of good deeds.