Here's a not-amateur historian who makes a similar argument:
Ó Siochrú, M., 2007. Atrocity, codes of conduct and the Irish in the British Civil wars 1641–1653. Past and Present, 195(1), pp.55-86.
Relevant quote: "This savage action [Drogheda] shocked opinion in Ireland and abroad, but by a strict interpretation of the rules of war Cromwell acted entirely within his rights. The commander of Drogheda, Sir Arthur Aston, refused a summons to surrender, thereby forfeiting his life and that of the garrison in the event of a successful assault."
Later he describes Cromwell as moderating his tactics in response to "facts on the ground": exchanging prisoners, and accepting the surrender of Clonmel. After Cromwell left Ireland, the war became bloodier.
Note that Ó Siochrú does not in general spare the English. He describes the "savage practices of England and Scotland" affecting Ireland in the 1640s, and gives examples of Irish prisoners of war being killed (in England), and of this being protested against by contemporary Royalists.
There's a huge difference between 'standard practice' and 'technically within your rights.' If it were standard practice, there would be no shocked opinion in Ireland and abroad.
Ó Siochrú, M., 2007. Atrocity, codes of conduct and the Irish in the British Civil wars 1641–1653. Past and Present, 195(1), pp.55-86.
Relevant quote: "This savage action [Drogheda] shocked opinion in Ireland and abroad, but by a strict interpretation of the rules of war Cromwell acted entirely within his rights. The commander of Drogheda, Sir Arthur Aston, refused a summons to surrender, thereby forfeiting his life and that of the garrison in the event of a successful assault."
Later he describes Cromwell as moderating his tactics in response to "facts on the ground": exchanging prisoners, and accepting the surrender of Clonmel. After Cromwell left Ireland, the war became bloodier.
Note that Ó Siochrú does not in general spare the English. He describes the "savage practices of England and Scotland" affecting Ireland in the 1640s, and gives examples of Irish prisoners of war being killed (in England), and of this being protested against by contemporary Royalists.