I have Amish ancestry on my mother's side and live among the Amish,as well as Mennonites and Dunkard Brethren today in central Pennsylvania.
I have so much to say on this topic, I hope I can keep my head on straight. I intend to write a book about this someday: "Amish, Mennonites and a Dried Cultic Root" or something like that.
First of all, almost all the Mennonites we know out here are related to each other. Some are 2nd and 3rd cousins. This is pretty close considering the rest of the world's gene pool. A very close couple to us are 3rd cousins on one side and 4th cousins on the other side. Her maiden name was Martin and she married a Martin. She is now XXXX Martin Martin. Her mother was also a Martin who married a Martin.
I have also seen this with the Amish where every family in our area either has the surname of Fisher or Byler. Every single one of those families are related and all their children are close cousins.
In our children's school (another anabaptist school) the majority of familes are all cousins. So far I have not heard of any intermarriage between the cousins but nothing would surprise me.
God never intended a Christian community to be a closed community. The heavy-handed tactics of the Amish and the more legalistic Mennonite leadership encourage people to remain in their communities, and marry within them, lest they literally "lose their salvation." Indeed, salvation is dependent upon exceedingly strict adherence to various codes of behavior and dress (I think dress is the most important, since Amish children drink and party, and often get pregnant. But they better LOOK right!)
Because of these tactics (which are very cultic if you look at what constitutes cultic actions of leadership), the Amish continue to remain Amish. As a result, few if any every join their groups from outside the original gene pool of a couple hundred years ago when they emigrated here. They are not just closely related; these people are more like siblings to each other. There is no strength in the gene pool and they are LOADED with deformities.
I see the deformed Amish and Mennos all the time. One poor Amish soul I have seen for years is highly cripped but manages to slide himself around; one poor Mennonite teenager had a cleft lip that his parents never sewed shut; he used to work at our local store. Another Mennonite boy has several fingers missing. A Horning Mennonite family we are close to just had a boy born with his feet on backwards. Another Mennonite family has a baby girl who was born blind and retarded. I am friends with a former Beachy Amish woman whose cousins are Maple Syrup Urine diseased. It runs in her family. And on and on. As diseased physically as they are spiritually; it is the mirror of their condition.
This is the result or turning away from the call of God to reach the world with the gospel. The Amish and Mennonites claim to be followers of Jesus Christ, yet the majority are insular, non-evangelistic, and incestuous. This is NOT the way it was meant to be.
If it were not for their incestuous marriages and cultic leadership, they would have died out along ago, assimilated into the rest of Christianity by bringing lost souls from all nations into their fold.
Moreover, to strain out a gnat and swallow a camel is a way of life. The Amish will pay to drive in people's cars or vans but they cannot own their own. Yet, some groups will allow tractors, as long as the rubber is off the tires. Horning Mennos who must drive black cars ONLY (to be "plain") drive around in shiny, beautiful, late-model Ford Mustangs, Acuras, Saturns. I always remark to my dear Mennonite brethren when I see their cars like this: "Oh, was a beautiful FANCY car you have!" It about stops them dead.
I could go on but then it will be my book. Someday.....