Separatists

Separatists are people who want to separate themselves from the mainstream establishment. In American history, it often refers to the Protestants who wanted to cut all ties from the Church of England, unlike the Puritans, who wanted the Church to conform to their standards.

The Pilgrims were Separatists who wanted to isolate from England, so they came to America to start a colony (Plymouth Colony) where their own religion was mainstream.

In modern Christianity, the Independent Baptist movement is the most active in practicing separation from sects with which it disagrees (which, for them, is virtually every other denomination -- and, in addition, another Independent Baptist with which they disagree).