Geopolitics don't enter into it.
In Northern Ireland, religion is correlated to political belief because the two major tribes are divided along those lines. Nobody who believes Northern Ireland should be part of the UK does it because of their interpretation of the Eucharist.
And you could say exactly the same about Islamic terrorists too.
Sometimes it has been part of the problem. It has encouraged the establishment of separate school systems for Catholics and Protestants and it has been used a tool by the extremists to give legitimacy to their violence.
Sometimes it has been part of the solution. It has given emotional healing to victims, and it has motivated community leaders on both sides to push for peace.
I'd suggest that the same is true of most conflicts that you think of as stemming from Islam.
What are you referring to?
> Religious fanatics are committing atrocities all over the world ... in the US they shoot each other and innocent bystanders or professionals
This is really just a platitude.
If we call anti-abortion attacks "Christian terrorism" (and we certainly should), then there have been 8 deaths in 16 years from fundamentalist US Christian terrorism.
Compare this to the nearly daily, and sometimes more, bombings, shootings, and executions carried out by fundamentalist Islamists. Adding up to thousands of deaths and hundreds of attacks every year, Islam is several orders of magnitude more violent than any other religion (specifically 10^4 or 10^5, depending on what you are comparing it to).
You can't forget the history of violence within the Christian world, too, where incidents like the St. Bartholomew's Day Massacre (http://en.wikipedia.org/wiki/St._Bartholomew's_Day_massacre) was extremely bloody.
I think it's more to do with Christianity being the majority religion in the west, where we have a cultural history of tolerating (even celebrating) differing opinions. Under a different set of circumstances, I could easily see Islam being more open and liberal (see how it used to be) and Christianity being more... like modern day Islam in many places? But that's not where we ended up.
If you're coming from an American perspective you've been taught that America is tolerant, inclusive, etc. but that's hard to argue in the face of facts. The level of racial separation is higher than in Apartheid South Africa, the income disparity is huger than in all but the most destitute banana republics, and non-Christian religions and non-believers are constantly persecuted by the Christian majority.
In the 1400s Islam was more liberal and open only because the countries in which it was practiced were relatively affluent. Christians at the time were waging bloody wars of conquest, especially the series of brutal Crusades to the Middle East.
If America had a demographic like Egypt, you would be seeing riots, blood in the streets, and major religious conflict. It's only because the people are too old to raise a fist in anger that there's peace. Baby Boomers are not going to riot no matter how riled up they are. Just look at how pathetic the Tea Party protests were compared to what happened in Tahir Square.
You can't look at religion through the lens of the last fifty years. Things shift dramatically and unexpectedly.
It's also easy to argue that a lot of Islamic extremism has been instigated by America and Britain because of the various coups they've thrown (Iran, Iraq) and oppressive regimes they've supported (Egypt, Saudia Arabia). Prior to that, things were a lot more orderly.
Look at how Lebanon went from a place of peace, tolerance and harmony, with a standard of living similar to Europe, to one of bloody civil war. This could happen anywhere when the conditions are right.
In regards to the rest of your post, I get the feeling you would prefer if western Christians were actually more violent, because surely each one of them is actually insane and will go Old Testament at the drop of a hat and start rounding up secularists...
What I'm really getting from it is that affluence leads to liberalization (in the classical sense) of religion, whereas the opposite of that leads to more fundamentalist religions. Which makes some sense - objective reality sucks when you are starving to death.
No religion has left their violence in the past, they have a book, hadtih/scrolls and vickers/mullahs which tells them they have a divine right to certain things like violent retribution for blasphemy or "blood atonement" and land titles, so violence will continue forever. Even buddhists are rampaging in Myanmar with machetes butchering up a sectarian storm.
And Buddhists don't have such a book, so I'm not sure what you're actually arguing here other than that religious fundamentalism is bad. Most religious people in the west already believe that (unfortunately not all of them).
Ireland is nothing to do with religion. It's a handy banner. It's all about British colonialism and oppression. Fuck, we sold the Irish as slaves to west indies planters. Of course it's geopolitics.
Religious fanaticism, however, does not equate to terrorism. It is a subset of the phenomenon, and operates on its own little set of utterly irrational rules.