This is a question in many people's mind and is sometimes referred to as the 'Homogenous Unit Principle', that is churches made up of all the same kind of people. Some people have argued that in the church we should be fully mixed and varied because, 'There is no longer Jew or Greek, there is no longer slave or free, there is no longer male and female' (Galatians 3.28), and that when we are in heaven there will be no divisions. Every tribe tongue and nation will be united around the throne (Revelation 5.9-13, 7.9 & 15.4).
However, this misses the point. Culture doesn't exist unless it's socially expressed. So every tribe and tongue will be present and preserved in its cultural identity (homogenous) whilst also being perfectly at one with each other (heterogeneous).
So we believe it is biblical to have both homogenous congregations (made up of similar kinds of people) and heterogeneous congregations (made up of differing kinds of people) in the same church. Homogenous congregations are not new of course. Sadly, many churches are already made up of one age group, race and social class (white, largely female, over 55) which can make everyone else feel shut out. Think of the average congregation at an 8am communion service!
Sometimes we need to start again for new sections of the community. However, every fresh expression of church needs to be linked into the wider body of Christ in a whole range of ways. No local church can ever be complete by itself. When we have the links, we have unity and also diversity.