"The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that doeth good." (Psa 14:1)
Let's assume, arguendo as they say, that there is no God. What then? Can I then say that the purpose of my life is as I define it? Can I say that what is good for me is what I define as good? Sure. Since there is no higher ontological category of being, there is no one superior to me in regard to defining either purpose of life or morality. At least, that's the way I would see it, if I were to say there was no God.
Well now, that sounds good. I can define for myself what I think is right for me, and you can define for yourself what you think is right for you. Now, what do we do with the sociopath? His idea of "good" may very well include lying, stealing, cheating, murdering, whatever it takes, to get what he wants. Well now, we can't have that! He might interfere with my "right for me" and your "right for you" so we have to gang up on the S.O.B and make sure that sociopath doesn't do something to interfere with our "right" to define what is right. Yes indeed, taken to the logical conclusion, if no one has the right to declare an absolute morality then man ends up by necessity being subservient to the will of the more powerful - usually the political collective or an organized crime syndicate (not that there's all that much difference most of the time). In other words, although I have a right to define what is good for me, I cannot exercise that right without the agreement of the collective society. That's a logical conclusion in direct conflict with the stated premise, and that is the hallmark of an irrational philosophy.
Well, perhaps we can get around that by saying that the rational thing for me to do is whatever it takes to increase my chance of survival and pleasure, and that means cooperating with the collective will in order to get a mutual benefit. Yep, if I were an atheist I'd be down on the front pew in Church every Sunday so that the "Christians" would leave me alone. (I have this suspicion that's precisely where the real atheists are.) The same would be true in a Muslim or Buddhist society. Go along with the majority religion to get along in society would be the rational conclusion. Only one hour a week listening to some nice music and a short sermon, and then I get to do whatever I want the rest of the time without having them bother me. It seems that living a lie would be the "rational" thing to do.
Fine, except, the premise is that my purpose, my "teleology" is to maintain my existence with the greatest pleasure. Having to give in to the will of others to get along is often in conflict with my desires. Furthermore, as any rational person knows, with absolute certainty, my physical existence is only sustained by work, and will come to an end with my death. To maximize my pleasure may very well mean that I should enslave you so that I don't have to work. But however I approach it, if continued existence with pleasure is my goal in life, my goal in life is doomed to failure. Yet, I am to pursue that goal anyway. That's irrational if you ask me.
So, I hear these folks say that they are not bothered by the lack of an after-life because they will live on in future generations, or because of the things they do that are beneficial to future humanity. Really? Well, to begin with, most people will leave this existence with only a few people even noticing they are gone. Most people will never make it to the top of society or into the history books. The odds of being remembered by future generations are so bad that betting on that is really irrational. I think you probably have a better chance of winning the lottery. But who cares? I wouldn't. If my consciousness dissipates at my death, there would be no "me" left to care whether I was remembered or not. It's a silly, emotional illusion to avoid the reality that we are born, live, and die with most of the world not even taking notice. The way I would see it would be that I wouldn't care at all what happens to the rest of the world ten seconds after I'm dead. After all, there would be no "me" left to notice, now would there? If I don't believe in an after-life it is irrational to even be concerned with what happens after my death. I'm certainly not going to be concerned about future human misery, environmental destruction, global warming, or anything else that doesn't immediately affect me. It would be irrational to worry about those things and a waste of my time to spend my life trying to solve future problems.
But who says you have to be rational? The atheists do, and are quite adamant about it. They complain that belief in God is irrational while they pile one irrational belief on top of another. Good grief. I would like to meet a real atheist some day. A real atheist would never try to tell me that I "ought" or "ought not" do anything. Since he is not ontologically superior to me, he has no basis for telling me that I ought to do anything. He can't even tell me I ought not believe in God without violating his own ontological premise.
That's why I say that atheism is a philosophical system for irrational fools.
Seems the Bible was right all along.