True missionaries seek out those who have never believed and teach them the Gospel.
They do not cozen people who already stand up in church every Sunday and pray the Lord's Prayer into joining a new sect.
If they believe that the very essence of the gospel is salvation through an antinomian loophole via the vicarious damnation of a divine scapegoat (and therefore that any and every religion that insists on human cooperation is the ultimate lie of "the devil") then they do.
How ironic that my own experience with the church might have been very different if I had only been born to a cannibal tribe in New Guinea.