cornelis, your analysis is brilliant. To carve out my own response to it, I'd start by saying there is a huge difference between a Sartre "trying [to] authenticate living for himself" and a christian "who yields to whomever or whatever is deemed to have it" [i.e., Life] -- which is ultimately God.
Sartre has no way to authenticate his own existential expeiences outside of his own personal resources. No wonder he is so anxious, so filled with distrust for the hellish "Other."
The christian, on the other hand, yields his existential experience to a judgment that is not conducted from his own internal resources. By this means, he is able to find both place and peace in this world.
But this does not mean the "christian-type mentality" will necessarily fall under the spell of the next slick shaman to come down the pike: Fundamentally, it seems to me the human spirit is quite discriminating about the things going on in its constituting environment (so to speak). IMHO.
It is precisely this putative human "instinct" for truth that comes most under attack these days -- so to get it to "doubt itself."
I'm sure in our modern world we will not lack for different points of view in regard to which is the "better" way to live a human life: Chronic existential angst, self doubt, and the ever-abiding keen skepticism about the motives, projects, and goals of the "hellish Other"; or an abiding sense of place and purpose in a Creation that is founded on ideas of love and mutual cooperation....
All of your comments are illuminating. I have nothing to add but "thank you" and a bump so others will not miss it!