I don’t, and I’m a nonbeliever. Self segregation (as opposed to the odious legal segregation of the Old South) builds community.
Why I think it's a bad idea:
(1) How successful are the Amish in evangelizing their faith? Very few people actually volunteer to be Amish largely because their communities are so deeply insular.
(2) As our Baptist friend pointed out, deeply sheltered kids who have never been exposed to moral hazard have an alarming tendency to either succumb or freeze like a deer in the headlights, not provide an inspiring witness.
(3) Communities like this (for example, St. Mary's in KS) have a tendency to begin considering their own internal community customs as doctrinal rather than discretionary.