I tend to see Nihilism as a necessary consequence of the rejection of the supernatural in all forms. If we’re to say that there’s nothing more than the world we observe, then a human boils down to a collection of semi-related particles doing whatever it is that semi-related particles do given the proper initial shove at the beginning of time. We can’t attribute a higher purpose or meaning to thoughts and emotions, because they really and truly are just chemical reactions. To accept anything else- that humans fundamentally have meaning- seems to me an equally large leap of faith as that which is required to accept the supernatural (and not all that different of a leap either- an acceptance of a non-physical reality on the basis of our desire for there to be one, rather than on empircal evidence). I'm not sure where exactly we can claim meaning from if we reject all such forms of faith.
I think by “meaning” here, I simply mean that we are more than a series of chemical reactions- and maybe more importantly, other people are also more than chemical reactions. We're not just random collections of particles, specks of dust in an infinite universe. The idea of humans having a soul seems dependent on this proposition, and I’m not sure I can ever get to any worldview other than strict Darwinian survival-of-the-fittest unless I regard humans as being more valuable than the sum of their parts. Obviously we could still have societal laws in place, since it’s (on average) in all of our best interest to have these laws, but I find that following this model on a day-to-day basis would lead me to become a sociopath, by the strict definition- a person whose behavior is antisocial and who lacks a sense of moral responsibility or social conscience.
There are basically two kinds of replies to this argument that Atheism necessitate Nihilism. This first is "I know, and I don't care". In this framework, our thoughts and feelings are themselves justification enough of our meaning. That is to say, the very fact that we seem to believe (or at least want to believe) that we have meaning is enough to give us meaning. In some sense this is true- purpose is entirely self-fulfilling. As I've said before, the definition of someone with purpose is someone who thinks he has purpose. But in another sense, this is really an argument of denial. The problem with substituting conviction of purpose for actual meaning is that we are left with no standard to judge reality. If all that's required to have a meaningful life is to construct a belief system that declares itself meaningful, then we've lost any basis for deciding which of the infinitely many such such systems to believe. This is perhaps forgivable if there truly is no meaning. But let us consider the terrifying possibility that one such belief system is true and the rest are not. If we want any chance of finding this truth (if it exists), then the "I don't care" framework is unacceptable.
The second reply says that Nihilism is not a necessary conclusion to draw. To quote the reply I got on the forum:
I disagree that God or nihilism are your only choices. If there’s not a God to give my life/actions meaning, it doesn’t follow that nothing can give them meaning. I happen to think that the best course is to provide one’s own meaning. Life’s most basic “meaning” is to preserve itself, in the most pleasant/satisfying manner possible. The meaning of a human life is to be the best human life it possibly can. Meaning is inherent in the thing itself, not imposed from outside.I think the problem with this response is that it's not dealing with the same definition of meaning that I am. This is an argument that we don't need a God in order to rationally take action in life. I agree with this premise. I don't think suicide is the rational conclusion of Atheism. But what I'm looking for is much more than a basis for taking action. I'm looking for a reason to consider humanity significant. I'm looking for justification of this claim my subconscious is making that humanity, right and wrong, love, life- all of it matters. I'm not sure how I can explain this properly, for I'm not sure I truly understand it myself. But something inside me howls for the knowledge that my life is worthwhile. It is worth the effort, the pain, the repetition of failure. There is some reason to endure these things more than trying to wring the most pleasure out of our brief existence that we possibly can.
I think this quest for meaning is a nonsensical thing to those who do not experience it themselves. It can't really be properly explained, because we can't even properly define what we're trying to get at when we say "meaning". But for those who feel it, as I do, it is plain as day.
Moreover, this argument seems to relegate humans to the same level as chimpanzees, or dogs, or insects- we could make the same meaning claims about them. I don’t see how we justify the fact that we value human life so highly. I don’t attach any importance to the oxidation of metal, or to combustion, or any other chemical reaction, so if the totality of a human is just a more complex version of that, I can’t bring myself to care about it (even if we give it the label of “soul”). Somehow its a much worse thing to interfere and prematurely end a more complex chemical reaction than it is to do so to a less complex chemical reaction? I don’t see how complexity maps to value.
I’m also not sure what the “best human life it possibly can” actually means. The word “best” implies that there’s something we ought to be doing? Something we can compare a life to to say whether it was lived correctly or not? This is essentially the Moral Law argument for Christianity.
I am of the opinion that with or without this need for meaning, a rejection of the supernatural in all forms leads to Nihilism as its only conclusion. The non-nihilist cannot give a reason why they believe what they believe that I find compelling. Social utility and evolutionary biology are not enough. A claim of meaning is a claim either of an extra-physical reality, or a deliberate self-deception for the good of ourselves or our species- simply act as if our arbitrary morality has meaning, and the world will be a better place. The only moral framework available to the Nihilist, however, is rational self-interest. And I know I don't want to live that way.