There are many illegitimate reasons to segregate churches, reasons which do not comply with New Testament principles and do not follow the New Testament example. Are there legitimate reasons to have separate churches? Three that possibly seem reasonable are distance, doctrine and language.
Distance, or different geographical location, is a reason that believers confined in mortal bodies meet together in assemblies near where they live. This is consistent with New Testament practice. Congregations of believers were formed and met in geographical locations where these believers were. Because of physical realities, distance or location, are and will remain a reason for the existence of separate churches until we all all located together as one flock under one shepherd.
Doctrine, different theology or creed, is a reason that believers meet in separate churches. Some of this is legitimate and some is not. Theological error, divisive disposition and moral failure are reasons for separation found in scripture.
Language can be a genuine barrier to worshiping together. It is a reason for the existence of separate churches in our time. In our area we have English speaking church and Spanish speaking churches. This is replicated for groups with various languages throughout the country. It is difficult to worship together if we cannot understand one another. Nevertheless, there are no obvious or outstanding examples of this that appear in the New Testament.
The last two causes of separation -- doctrine and language -- can be alleviated, There are real doctrinal differences among Christian believers. These should not be ignored or overlooked. We don't just give up our doctrinal distinctives to pretend to have unity. But by endeavoring to come to the unity of the faith we can try to dispel those differences. Further, we should consider whether some differences are doctrinal or personal preferences for things not addressed by doctrinal orthodoxy. If we must separate over doctrine or related considerations, we should, It should be the last resort.
The lack of division by language may be partially explained by a widespread common language across the Roman Empire. Yet some of our current separation due to language might be explained by comfort and ease rather than necessity. Do we want to meet together? Is it more important than remaining segregated from our brothers and sisters by language? If so, it could be alleviated by preachers who speak both languages. Both could preach to the entire congregation, rotating who preached in what language and who translated into the second language. Further, believers can begin to learn one another's language if we place high enough importance on unity.
So that leaves the first — distance — as the main reason to have distinct and separate churches. There are biblical reasons and examples for local churches in local areas where believers live. If doctrinal error is not an issue, we should meet with the believers who are near us -- as opposed to driving past meeting places to get to another we "prefer". Otherwise shouldn't believers come gather together in the name of Jesus? Even the legitimate separation of distance can become an excuse to not meet with other believers who are too far away. While we may not be able to regularly meet together, we should be aware and at times meet with believers across a broader range of geography. It is intriguing to read the New Testament and see how much Christians across the Roman Empire knew about one another (with very few communication options compared to what we have today).
What do you believe are legitimate reasons for separating/segregating our churches?
Quotes from Review: Come, Let Us Reason Together: The Unity of Jews and Gentiles in the Church by Baruch Maoz
"Ethnicities, doctrinal issues that do not reflect on the glory of Christ, cultures, and human interests must not be allowed to define congregations. To transgress this standard is to promote a man-centered gospel that places human interests on the throne where God in Christ should be sitting. It is to forsake the biblical focus that should characterize all who seek to serve God. (p. 159)"
"Seeking the comfort zone, we avoid the tensions that a multicultural, multinational, multilingual, multi-layered church would posit. (p. 168)"