" it is appalling to me that the British chose to execute the leaders of the Easter Rising"

Ill advised certainly, but the penalty for treason in time of war is death. The leaders of the Easter Rising had been in contact with the German Government since the outbreak of hostilities in August 1914. Immediately before the Easter Rising a ship carrying German arms was intercepted off the coast of Ireland and Sir Roger Casement was arrested after having landed on Banna Strand from a German Submarine.

In the aftermath of the Easter Rising some 3,500 were arrested and held, Courts Martial passed 90 death sentences, commuting all but 15 of them to five years imprisonment, those sentences ended up as being 1 year.