De Valera should have taken Northern Ireland when it was offered by Churchill during WW2 in return for the south abandoning neutrality!!
Only thing is Churchill never offered it, with any degree where he could be trusted to deliver.
Admiralty was clear that while Eire joining Allies would have some use, it reality it would cost more because of the need to scatter defensive forces even further across more territory especially when they needed it just to protect home ports.
Luftwaffe Condors used to bomb Scotland and follow western Irish coast before landing in Brest, means all areas of Eire were still attackable.
Population of Eire I believe overwhelmingly supported neutrality during WW2, their war of Independence and Civil War were still in close memory.
Would London have potentially lost the benefit of the thousands of Irish men coming over here to join up or the thousands of men who came across to labour in factories or building airfields ?
As to Adams, believe its political. It also means every member of armed forces that has been involved in killing / injuring a civilian is now under same basis of being chargeable for what they did then as well as those who gave orders.