I want to clarify that, first of all, I mean NO offense to anyone currently struggling with depression. I have personally been in that dark place, although ironically it was largely because of my extremely conservative and ultimately self destructive belief system.
With that said, the person who sent this letter to CMI had just come out of a period of depression so severe that he considered suicide. Religion really might have given him a reason not to kill himself, but converting to a religion because you feel so despondent and empty that it feels like life is utterly empty and pointless is not conducive to objective reasoning. It is *extremely* inappropriate for a group like CMI to hold him up as an example of an atheist convert who agreed with their philosophy when he converted out of pain, and to a faith that is likely to hurt him more in the long run.
Ultimately, a person grasping for any branch to pull themselves out of a raging flood is even going to be willing to grab hold of one that isn't very firmly anchored. While I wish Justin S. the best, the most likely outcome of his conversion is a discovery that it was not a long-term solution. Atheism and even nihilism don't drive people to suicide on their own. Existential crises that *do* sometimes come with atheism are generally uncomfortable growth experiences when they aren't complicated by psychological illness. Depression or anxiety can seize on those things, particularly on feelings of existential meaninglessness, but the depression has its cause elsewhere.
Conversion might temporarily assuage the symptoms of depression, but its long term effect is likely to be negative. The sort of evangelicalism advocated by organizations like CMI can give people a positive effect of making them feel important and good thanks to the effect of the atonement (or no one would convert), but ultimately, the bad can easily start to outweigh the good. Justin S., at some point, is almost certain to struggle with depression again, only this time, it will be complicated by the fact that he believes it's a sign that he might not be truly saved because God isn't giving him the "gift of hope". Beyond that, secular therapy will be more difficult for him to receive, because it generally includes treatments outside of what fundamentalist Christianity allows. Given the attitudes of many more conservative Christian therapists, he could receive therapy that hurts him worse than he is already hurt.
Again, I wish him the best, but as someone who fell into fundamentalism thanks to psychological difficulties myself, Justin S. is not on a good path right now. When I walked down that same road, I went from a healthy, happy 18 year old to a nervous, morally confused wreck in three months. Believing that the slightest misstep or even feeling of emotional torment might mean you haven't been saved (or might cause you to lose your salvation) and that you will burn for all eternity in unimaginable agony while God watches you and laughs leads you to fantasize about never having been born. I would have been suicidal, if I had thought that death would do any good. He needs help that he may never be able to get.