The one true Church IS COMPOSED OF ALL BELIEVERS IN THE LORD JESUS. It is made up of all God's elect — of all converted men and women — of all true Christians. In whomsoever we can discern the election of God the Father, the sprinkling of the blood of God the Son, the sanctifying work of God the Spirit, in that person we see a member of Christ's true Church.
But would we be satisfied with the value systems of the thief or of the cannibal, it being the case that we could well be the object of their attentions?
This is the painful difficulty generally ignored by ethical relativism and by the postmodern approach of “live and let live”: one may find herself devoid of possessions and one of the ingredients of a stew if certain value systems are given legitimacy.