The West Brit element in Ireland love mass immigration because they always want a way to dissolve the power of the Native Gael in Ireland. The West Brits have an actual political motivation for promoting mass immigration. Except for Alan Shatter, of course, who has his own distinct tribal hatred to indulge in.
The next group are the trendy lefties like the Trots and Adamsite Sinn Féin. Like the Labour Party in England, they see the only way they can ever get elected is by changing the population of Ireland. They hope that by encouraging mass immigration and shouting down (and even beating down) any Native Irish person who objects to the invasion and plantation of Ireland, and the immigrants will be forever grateful to them.
The next group of mass immigration mongers are the cheap employers - like Michael O'Leary, and the landlords \ landowners. Cheap labour who will shove up rent and the price of land is a boon to this criminal element. They are mostly apolitical. They only care about easy money.
The next group is a group that has always hated Ireland because they think Irish society repressed them sexuality. There is now huge sexual abuse of migrants by middle class Irish men - and some women too.