where does this leave the parent who, because of dissatisfaction or disillusion with "Christianity", snatches their child from the greater "flock" of the sheperd?...
We stand alone before God.
If we allow others to think for us, judge for us, limit us to who we can and cannot love and forgive or hate and shun--we give up what makes us unique. We become a thing and not a person; a tool for others without a mind.
A child has a unique status in society. A child is expected to be their own person____some day___yet, a restraint is placed upon that child under the custody of the parent.
Society and law assumes the child's best interest are sought by the parent. If it should be demonstrated convincingly that the child is in jeopardy---steps are taken to remove the child from the aberrant parent and a substitute custody is awarded.
In the case you cite above----A parent who leaves the congregation for cause has made a decision for themselves and their child's well-being.
If it is a decision made in good conscience with informed judgement it should be an improvement and not an oversight.
But, the mothers in the Mormon compound were certainly spiritual minded people whose personal consciences had been short-circuited by indoctrinations. The individuals ceased to be individuals. They became drones for those in power who wielded scriptural authority in bad faith.
The JW's who allow their children to die by refusing necessary medical procedures demonstrate that a corporate judgement cannot replace the individual conscience or disastrous consequences will follow.
That is why each of us has a brain and a moral imperative to make our own decisions regardless of the claim to authority made by others.
Parents have a double imperative to make the best informed decisions rationally and without prejudice.
I hope this answers your question.