The atrocities are remembered in Ireland as atrocities all the same.
> James Joyce wrote in Ulysses, 1922, “What about sanctimonious Cromwell and his ironsides that put the women and children of Drogheda to the sword with the bible text God is love pasted round the mouth of his cannon?”
> Winston Churchill’s view in The History of the English Speaking Peoples: The Age of Revolution, 1957, is perhaps less artful, but succinct: “By an uncompleted process of terror, by an iniquitous land settlement, by the virtual proscription of the Catholic religion, by the bloody deeds already described, he cut new gulfs between the nations and the creeds…. Upon all of us there still lies ‘the curse of Cromwell.’ ”
Is there a specific fact, letters etc. from the time you’re arguing against? From what I recall his barbarism was seen to stand out at the time in England and Ireland. He used it as a type of shock and awe, so when arrived at the next town they’d just surrender or flee.
Just that the subject is the politics of the time (i.e. what were the people at the time arguing about - what was that "legacy" they were looking to influence), and that modern authors are looking at things from a different perspective.