There is no happiness to be gained from the rejection of a hypothesis, nor is their sadness. It is merely what it is, a rejection of a theory.
Atheists do not simply reject the Christian God, or religion, they reject the premises on which religions are founded.
A-theism: reality without higher powers, without ideals of humanity, heaven, or hell. It is a reality based upon the idea that we are simply what we are, when we are, and what we are not when we are gone.
Christians have difficulties detaching themselves from their religion, and that is why questions like this one exist. It is not that atheists hate God, or dislike religion, they simply cannot attach themselves to an existence based upon illogical and unproven ideas.
Just the same, many atheists reject common principles in advanced science, like the Big Bang Theory, or String Theory, because there is no satisfying proof of their existence.
In the eyes of an atheist, God and the Big Bang could be the same thing, a theory.
And when an atheist thinks about death, they do so with the reality that there is nothing after wards. So the real question is how can you care about something once you are dead?