As I got older, the futility of living and the idea of nonexistence grew. They permeated my regular modes of thought. Although I began basing my system of morality on generally utilitarian principles, I could not justify acting upon these principles as a means to reach some kind of intrinsic value; I opposed utilitarianism's principles of happiness because I did not believe happiness had value in and of itself. Instead, I acted on utilitarian ethics because I attached a negative value to human suffering. I had accepted the idea that nothing, by our own definition of the term, has intrinsic value because anything that would have intrinsic value is temporary; our happiness ends and it becomes as if happiness never happened in the first place. The utilitarian definition of intrinsic value, then, becomes whatever supplies permanent happiness. Because nothing supplies this, we are plagued with knowing our happiness and lives are limited. This knowledge hinders how happy we can feel, especially when compared to those who either tend not to think about death or believe they will not die at all.
As I grew even older and went to college, I began to gradually appreciate my experience of living, and I believe it is likely I appreciate life much more than the average person. Appreciation is not the same as happiness, however, and the thought process usually goes something like this: 1. Spurt of happiness 2. Recognition of temporariness of happiness 3. Loss of happiness after realizing it is temporary 4. Appreciation for the ability to experience happiness.
Essentially, appreciation is knowing happiness will end, and number two and four in the thought process go hand in hand. Logically, those who are happiest should dislike the idea of no longer existing the most, as they lose the most upon dying. Whether one loses a positive, happy experience or the potential to obtain such experience, we are undoubtedly afraid of losing everything should we value anything even in the slightest.
And so to the atheists who claim they are comfortable with the idea of dying, or that the idea of dying does not hinder their ability to feel happiness to the fullest extent or feel both happiness and appreciation at the same time, I call BS. We like the idea of eternal life—we just cannot bring ourselves to believe in it.
Here are a few Wikipedia pages with information on the references in this post: