Your use of 'they' implies the same people who are blaming the problems on another country (nobody is doing that) are the same people who were the oppressors in Ireland. I'm not sure why.
My use of Ireland referred to the whole island and asked whether or not the absence of the country and thereby these divisive but ultimately galvanising differences in identity in OF fans would have changed the Scottish football landscape and how. It's not serious, just a ponderance of an alternate reality.
It's fair to say these issues have acted like a shot of steroids in the arm for both clubs, with it forming a stronger bond in the minds of fans as they feel they have to protect cultures and uphold traditions which are under attack from the other side. Things that fans of any other club simply don't consider when supporting their team or thinking about football.
Hmm, Celtic still would have been formed* by Irish immigrants and I'd imagine there would still be anti-Irish/anti-immigrant sentiment? Would Rangers have still taken on the role of Scottish representatives of the British state without Protestantism? Like @Jacky1990 I wonder how much of it is, truly, down to religion or if that's simply just another weapon to use when attacking one another.
*Actually, I realise now the basis for which Celtic were formed and so perhaps they wouldn't have existed without religion. I wonder how the absence of religion would affect the numbers of Irish immigrants, how they were perceived and whether or not a football club representing them would have come to be?
Without religion I'd still expect them to have become the "fierce" rivals they are today, that's why I said Ireland and not religion. But then again, who knows? Without Ireland, Celtic wouldn't have existed and Rangers would have had no reason to get out of bed in the morning. Maybe Queen's Park and Partick Thistle would have become the OF and a poison in our game.