What Biblical basis do "separation traditions" have to support their beliefs? There are a variety of Christian traditions that involve some level of separation from the world - monasticism, the Mennonites, Amish, Shakers, Quakers, etc.

We are told in the New Testament to be "separate from the world" and to be "unstained by the world".

We are also told to "go and make disciples".

I know that the Bible does not contradict itself.

How do the "separation traditions" (for lack of a better phrase) support their [sometimes full] separation from the world with the other (sometimes apparently contradictory) commands given to Christ's followers?
It comes from the idea of sanctification.  Sanctification is from the Latin sanctificio, which means "set apart".

This concept is also reflected in the Bible.


  John 17:16-17 (NIV)
  They are not of the world, even as I am not of it. 17 Sanctify them by the truth; your word is truth.


These groups take this (along with other verses) as an indication that they should separate themselves from the world.  

One other verses supports this concept:


  Romans 12:2
  Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is—his good, pleasing and perfect will
  
  John 15:19
  If you belonged to the world, it would love you as its own. As it is, you do not belong to the world, but I have chosen you out of the world. That is why the world hates you.