Cultural similarities? Tell that to the people of Northern Ireland. You'd be doing well to find two competing groups who are culturally so identical, yet who fight so much.
In any case, it's probably worth nothing the cultural breakdown of Irish immigration. According to the CSO [figures are for 2002, most recent I could locate easily]:
37% of immigrants were Irish.
10% of immigrants were from the UK.
12% were from the EU-15
(this was pre-englargement)
4% were from the U.S.
And the remaining 34% were from the rest of the world, a large portion of which presumably have come from Eastern European countries which are now part of the EU.
So, all in all, the vast bulk of our immigrants come from a culturally very similar group.
That's not to say, I agree that "cultural compatability" is particularly important or desirable per se. Just illustrating the facts.
Source:
http://www.cso.ie/releasespublications/ ... g_2002.pdf (see table 8)