I think it is true that geography and parental influence play a large role in one's faith, especially initially. But why should that bother the believer?
Is a Christian comfortable with the fact that if they grew up in Iran they would be equally (if not more so) devoted to Islam?
I imagine that they are, yes. The Bible says that no one can come to know Jesus unless God the Father has drawn them (John 6:44). To some, this could indicate that God chooses who will come to know Jesus. So if there are Christians in Iran, it is because God drew them to Jesus. If they remain devoted to Islam, then they were not drawn.
This could be the standard apologetic for your question of whether a Christian should be comfortable with the fact of geographic influence. To the Christian, you see, it doesn't matter where one is born. If God chooses them, they will hear his message about Jesus. The Bible also tells us that Jesus is the good shepherd and his sheep hear his voice. Those who aren't his sheep don't hear his voice, I guess. Does that seem exclusionary? Sure does, but there it is.
That type of arrogance is what always gets me related to many of the Christians I encounter on my travels through the Upper Midwest and the South. That somewhere along the line, "God's chosen people" went from being the Israelites to being Americans. The New Testament pre-dates there even being a United States of America by 1,400+ years. And the Old Testament was written thousands of years earlier (or at least the original stories that were passed down verbally before being written down were). Americans think they are the center of the planet/galaxy/universe, and we're raised that way from the time we can barely walk. So why would American Christians not think that we're "God's chosen people" too?!
The other thing that always gets me? Millions of images of a "white Jesus" that exist throughout church after church across the country. Inherited from hundreds of years of "white Jesus" being on full display throughout Europe. Then some Christians even going so far as to claim that white people of European descent are "God's chosen people," and warping scripture to treat others as second/third class individuals. I was attending a Bible study with my wife a couple years ago...where they were discussing a series called "The Truth Project." Basically,
"atheists say __________, and here's why atheists are wrong." The leaders of the group, along with 5-6 of the other ~20 attendees, were railing against revisionist history. Lots of teachers at public school in the crowd, lamenting what children are(n't) being taught in public school. People writing God out of the history books related to America's Founding Fathers.
I politely raised my hand and asked:
"What color was Jesus' skin? What color was Jesus' hair?" How tall was Jesus?" To which most attendees looked at me like I had just landed in a space ship from Mars. So I clarified my point.
"Given the region of the world in which Jesus was born, at the time He was born, what were his likely physical traits?" Of course, they might have countered with the fact that Jesus' "DNA" wasn't dependent upon Mary or Joseph, via immaculate conception. But even with that in mind, if God were sending His Son into Israel ~2,000 years ago, what did he likely look like? I'd have bet good money that he wasn't white, ~six feet tall, with straight brown hair and blue eyes. But how is Jesus depicted in just about every picture, altar, stained glass window across the United States and Europe?
Of course, then I reminded folks that we need to work on the planks in our own eyes before we go criticizing the specks in other people's eyes. Related to "revisionist history." But that got me off of a few people's Christmas card lists as a direct result.