I Don't Even Know What To Say

A recent post on Reddit in the r/DebateAChristian subreddit asked this question:

"Of all the arguments you've heard, which is the one that keeps cropping back up in your mind as a potential problem for your beliefs?"

The response from one user was perhaps the saddest thing I've ever read (emphasis mine):

"None. Before I was saved, there were many, but afterward, I couldn't disbelieve if I wanted to. The hardest thing to believe was that my very ability to reason was flawed. Once I got over that, the rest was very, very easy.I still have doubts, but they are doubts like "Am I sure that I am saved?" or "Am I certain that is what the Bible is saying there?" Also, there are times when, due to my skeptical past delving too far into philosophy, that I begin to doubt all existence as a whole, but I find even the nature of existence as less tangible and true than I do my faith."

I really don't know what to say to this.  People are being taught this, apparently.  They are being told that they cannot think.  That their ability to reason, to make sense of the world, is simply wrong.  And of course, once you abandon any trust in your ability to reason, once rationality and critical thought are left behind, everything else is ridiculously easy to swallow.  You'll believe anything you're told once you've been convinced that you can't even make a reasonable objection.  And this walls your mind off from any debate, any discussion; the things you've been told are right cannot be challenged, and nothing will shake your faith because, obviously, nobody else can reason either.

How did we come to this?  How did fideism become so powerful?  The only advantage that we have, the only thing that makes humans the most successful mammals on the planet, is our ability to think.  That there are people who give that up, who willingly subjugate themselves to people who do their thinking for them, is depressing and frightening.  This right here?  This is why I fight against religion.  No, not everyone believes this kind of thing.  Not all religious people abandon reason.  But this mind virus, this cancer of thought, this deep wound inflicted on the human psyche, is empowered by religion.  It is the environment of faith that allows this disease to flourish.  And it has evolved a powerful, nigh-unbeatable resistance to the only weapons we can use against it: skeptical inquiry, rational thought, and evidence-based reasoning.  I don't really know what to do.  Anything I can say to this person will simply sluice off, like water off a duck.  What do you do when religion ends the conversation before it can start?