Nihilism-- the belief that there is no meaning to life and no spirit world-- is the most logical thing to believe in. Religions are contradictory and they all claim to be the one truth. Nihilism makes sense because it denies all of the contradiction. --Someone who's name I can't remember. This is a REALLY paraphrased summary of a pretty long post.
There are a spectrum of belief systems, and nihilism has the Occom's Razor advantage of being the simplist. It wipes away all the questions people have about a spirit world and about God and about the meaning of life in general-- except personally. In all metaphysical areas-- and frankly almost all ethical ones-- there can be no discussion between people. What anyone says about these subjects is ultimately correct for them, personally. Of course, we will have to throw out most science as well, because studies have shown that most studies are ultimately subjective-- including the original studies that showed that.
Nihilism is simple-- but so simple that no one wants to accept it. Nihilism questions all speculative truth, but without speculative truth there would be no law of gravity, no shuttles in space, no cell phones, etc. We gotta start somewhere, science says, so we begin with a theory that seems reasonable and then we go out and either prove or disprove it. Nihilism, as a belief system, has been around a long time-- not the longest, spiritism has that distinction-- and it has been discussed by people for longer than philosophy has been around. This gives it the distinction of being the most rejected belief system that has ever existed.
Why has Nihilism been rejected to such an amazing degree? First of all, because it doesn't meet people's inner need. Athiestic existentialism is simply giving a needed face lift to nihilism, because if people were going to believe in nothing, they still need to believe in SOMETHING, even if that something is only in their own personal experience. But most people aren't ready to deal with such logical hoops, and they need to believe that their life has some meaning. They need to believe that there really is justice, although they don't see it. They need to believe that there is still a chance for inner peace, although they don't experience it now. They need to believe that somehow there will be a time and a place where they will be secure, even though that doesn't exist now in what they currently experience. Frankly, nihilism doesn't meet most people where they are, it doesn't meet their needs.
Secondly, nihilism's simplicity is at first disarming, but after reflection it is simply unsatisfying. Frankly, the universe and our personal experience is more complex than nihilism will admit. There is much that is unexplained, and there is a universe-- possibly multiple universes-- of knowledge that humanity will never grasp. The human brain is finite, and yet nihilism implicitly claims that human knowledge is all that is significant to humans. Because we cannot "prove" God, therefore God must not be significant. Because we cannot fully grasp a spirit world, it must not exist. Because we cannot, as humanity, decide on a single meaning of life, therefore there must not be any.
It's kind of like the people who saw The Wall on LSD. Just because they couldn't understand any meaning, they assume that the writers and director of the Wall were on acid when they made it. Just because a minority of people cannot grasp any meaning, and others disagree on the meaning, it is a leap of logic to determine that there is NO meaning.
I would understand if someone explored a number of belief systems-- really understood and experienced them-- and then determined that there must not be any meaning after that. At least they explored some of the possibilities. But to say, a priori, "there is no meaning" without actually, honestly, exploring the possibilities of meaning is self-deception. This is not the scientific method. It is not critical analysis. It is just another religion. And it is a greater leap of faith than most religions out there. At least most religions are fairly existentialist-- it is based on a personal experience. But most nihilists are anti-existentialist, it is based on NOT having an experience. It may be trite, but it is true that if you look for nothing, you will certainly find what you were looking for.