The highwayman exploits set in Ireland and Scotland that Michael Martin related in his confession need to be viewed in context of a long tradition of romanticizing the image of highway robbery (particularly in Ireland) as an act of resistance against wealthy overlords and their agents. This heritage is not unique to Ireland (the English Robin Hood is the most recognized example), but persisted there with new examples found in each generation through the 17th, 18th, and 19th centuries.
Examinations of this tradition can be found in Ray Cashman’s books and articles, most concisely in:
Cashman, Ray. “The Heroic Outlaw in Irish Folklore and Popular Literature.” Folklore 111, no. 2 (2000): 191-215. Accessed May 6, 2021. http://www.jstor.org/stable/1260603.
The abstract to the above article reads:
“As a symbolic figure in Irish folklore and popular literature, the outlaw embodies folk morality in conflict with the self-interest and inequity of the state. In the aftermath of British colonization, the Irish outlaw is represented as more than a criminal. He provides a hero through whom ordinary Irishmen and women can vicariously enjoy brief victories, and imagine their collective dignity in the midst of political defeat and its consequences. Legends, ballads and chapbooks portraying the outlaw are the products of hard-pressed people representing themselves to themselves, reflecting on their strengths and weaknesses, and contemplating issues of morality and justice.”
More articles on Irish outlaws: