I've read every post in this thread with careful attention, & 1 thing that IMHO needs to be pointed out is that, like the ancient Greeks, the post-Crusade Europeans, & the American Indians, we Celts have always been much better at fighting among ourselves than uniting against the common enemy. It has been & will continue be our downfall.
The Greeks couldn't even send a complete army to Thermopylae to oppose Xerxes. It fell to a Spartan king & 300 of his men to sacrifice themselves in order to galvanize the city-states. They couldn't even raise an army to invade Persia until they were united by an outsider-- Philip II of Macedon.
During the early Crusades Europe was reasonably united against Islam, but then Christendom allowed the Holy Land to fall, they failed to unite against the Mongol invasion, & they allowed the Muslim conquest of Constantinople & the Balkans all the way to Vienna.
...and how different would the American westward expansion have been if the Pawnee & the Crow hadn't served in irregular bands under US Army command, if Apache scouts in blue uniforms hadn't fought against their own people, & so forth?
Likewise, the English use of Scottish mercenaries against the Irish, & of Irish against their own people, is notorious. I've often thought how different Celtic history might have been, had the Celts been united instead of divided.
So perhaps the Jєωιѕн influence (& as 1 poster has pointed out, the black influence) is as pervasive & corrupting as you say that it is. I have no trouble believing it, but somehow I doubt that's the underlying problem.