Considering Ireland (except Northern Ireland) is now widely accepted to be independent of Britain, doesn't that mean any "treason" supporting that should also seen as acceptable, and Casement should be pardoned from his treason conviction? To maintain it, implies that Ireland really shouldn't be independent, and that anyone still supporting it is also guilty.
It sounds silly, but that's how it really is. Treason is often a crime with the harshest punishments, yet also one that's most unclear if it's very bad or very good. Somehow it doesn't seem to get the attention it deserves as immoral law.