Re: "“All desire is the inappropriate substitute for the desire to be at one with God.”"
What's scary about it... Let me break it down:
1) The statement is on the face of it absurd. For instance, your desire to not be attacked by a swarm of bees isn't an inappropriate substitute for the desire to be at one with God.
2) The statement suggests that your life, the lives of those around you, and this world, are all irrelevant: only God matters. That way ISIS lies.
3) The statement suggests you should feel guilty for, for instance, wanting to own a house, instead of donating the money to <insert church>. Your desire to own the house is inappropriate.
4) The statement implies that individuality, i.e. having any goals except those imposed by your church, is inappropriate. That way Jonestown lies.
Basically the statement is the linchpin of the very thing you agree is scary: religious authoritarianism.