The Anglo-Irish War and the Irish Civil War were horrible catastrophes where men did horrendous things. But one does not need to see the sin to know man is a sinner.
There is an argument to be made for modern historical interpretation: for showing the rough reality of war and peace, politics and diplomacy, or showing the sorrow of a mother who lost her sons on D-Day or the twisted side of treason. Something gets lost in the translation, however. There is an indisputable glory in war. There is brotherhood, self-sacrifice, the stunning ability for one man to change the course of the world. All of that gets lost when you focus on the carnage and the fear.
That is why human memory works the way it does. The means get forgotten when the ends are worthy. And it is the ends that must be remembered. Not only that good and noble men sometimes do terrible things to achieve good and noble ends.