What I find troubling around here is this make mediocre peace of saying that everyone is entitled to their own truth. Live and let live is a position of resignation. If you have concern about truth, a proper view of reality, then such talk is not acceptable. Well that is my take at least.
In terms of Christianity, I was very troubled by what I read in the book, "when God talks back" (the lower case is how the book does the title), in that how evangelical Christians will end up doing visualization and other mental tricks and create experiences for themselves they believe are interaction with God. Such individuals then develop a dogmatic certainty that their experiences of God. And then, when reality doesn't correspond, they practice a bunch of mental gymnatics to justify why very detailed prayer didn't come off as expected. They will also fracture their thoughts in their brains that some thoughts are somehow of God directly. I won't speak on maybe there is valid thoughts lining up with the Bible, but it is taken as God directly interacting. In this, the push for "faith" also made a mess of lives.
As for why people try to do it, you have individuals who got disillusioned by certain religion, and then they take their same dogmaticness they had when in the religion and then go on a crusade for meaning, trying to deconvert others. It is partly insecurity in what they have, and secondarily, not knowing what else to do with their being. Some others, n the high end intellectual side, end up making a living of sorts writing books on it. They are assassins in the manner that Bill O'Reilly mentioned. And there is also an evangelical/fundie branch of atheism that so much wants something to be there that they go off and make a religion of a lack of belief, in hopes that, somehow, they can form community and have common values seen in religion, while having a basis of common unity on nothing (aka, a lack of a believe = nothing).