Is faith necessary for man to survive / why is existentialism valued if it is unsubstantiated?

I'd like to point out that I have basically no knowledgeable background in philosophy, but this question has been troubling me as of late, and I need an informed take on this. I was watching a video by Dr. Jordan Peterson, a professor of psychology at the University of Toronto (who is quite more well known as of late) on the psyche that motivates school shooters. It can be watched here. He spoke about Leo Tolstoy's spiritual crisis, which he wrote about in A Confession, where he slumped into a deep depression and at one point concluded that the most logical and bravest thing a man can do is commit suicide and murder, from what I gathered. He later realized, which recovered him, is that faith in something is the ultimate meaning in life, and the key to not cause man's fall into despair. This deeply troubled me. This was an extremely clever person, and far more philosophically in tuned than I, basically saying that without some kind of religion or belief in what is not concrete that man will slump into hopelessness and prefer to be dead. I desperately want to label him as flatly wrong and ridiculous, but I cannot deny his reputation. Carl Jung is another example. From what I've gathered, it seems that very clever people, more informed on philosophical matters than I, have concluded that life is meaningless, or meaningless unless I believe in the infinite. This is extremely depressing, and I desperately want to believe this is not true. I suppose I am in fear of being 'indoctrinated' in this 'correct view of the universe' and slump into some depression that will deprive me my ability to attain my goals via an existential crisis. Is it really true that life is this bleak? I know this sounds naive, but I'm uninformed on this subject? In my view, I've thought along William James's lines, that nihilism is a byproduct of depression and not some arrogant declaration of understanding of how the universe works, and I still do -- but it still bothers me that people more knowled