This has not been true in my experience. I chose atheism in order to resolve the internal conflict between the theistic philosophy I was raised in with the truths I have found for myself in life. The shadow theism has left on me from the first twenty years of my life is something I may always be saddled with. Atheism is a way to help make sense of the real world by contrasting theism with the pragmatic truths of modern science and philosophy.
Many people are raised in a secular household or a home or community where religion is not emphasized, but this is not the case for most in America. An overwhelming majority of people in The U?S. consider themselves to belong some sort of Christian religion - at around 78%.* - so leaving theism usually involves a choice, often a difficult choice that can feel like jumping off a cliff.
I only made the difficult decision to leave the Mormon church after the flaws in theism became so overwhelming that I could no longer deny them. This came after many years of prayerful and thoughtful study. Ultimately after weighing all the the evidence the "problem of evil" convinced me that all theist churches are seriously flawed and insufficient to provide a true picture of reality.
So what do we get in return for all our tears and being ostracized from our former social groups? Why are so many people willing to give up so much for their belief in atheism? After all, if it's all just a myth why not just go to church and not upset people?
Truth
A devotion to a sincere understanding of the truth was essential when I chose atheism. A frustrating thing about theism (or any other organizational structure based on absolute obedience) is that doubt and questioning are often met with admonition or ridicule. The problem with this is that truth can never come without questions. Often the key to understanding is knowing what question to ask. Being unafraid to ask questions about God and people who supposedly speak for God allow a greater understanding of human society and history.When I chose atheism, my understanding and wonderment at the beauty and complexity of the universe increased immensely.
Peace of Mind
The ideas of an afterlife or a watchful God seem to provide a peace of mind to theistic people. This can be true to many, but often that peace is actually willful ignorance reality. A true understanding of positive situations allows greater joy, and a more honest understanding of negative situations allows the discovery of better solutions. An ability to understand and rely on concrete things allows a greater sense of well being and peace. No longer are you afraid of monsters, devils, or ghosts when you understand how human expectations, dreams, and fears can alter our perceptions.When I chose atheism, I was no longer afraid of the dark.
Appreciation of Life
The hope for a life after death is shared by almost everyone, but unfortunately there is no compelling evidence that this is true. Theism unfortunately uses promises of riches and/or rewards in the afterlife to pay for actual work and riches of it's members in this life. Without reliance on the promise of an afterlife, the true value of our lives becomes much more clear. No longer can wars and murder be justified by a "kill them all and let God sort them out" philosophy. With an increased value on life, death becomes a much more devastating loss, as it should be. The uniqueness and beauty of a human personality is the most valuable thing we have ever discovered in the universe.When I chose atheism I gained a greater appreciation of life and the short time we all spend in this world.
Regardless that atheism is a doctrine of belief that there is no god, it still represents a positive change for those who have discovered that theism is an unsatisfactory theory of reality which simply does not account for much of the knowledge and discovery humanity has accumulated over the last two millennia.
Despite it's relatively recent schism with religion, science represents the best and most solid knowledge about life, humanity, and the universe. There is no ancient knowledge that religion possesses that is not also included in science. Religion has forfeited the ability to tell humanity about our origin, our character, or our path to happiness. I look forward to the day where people do not rely on ancient stories or simple "God did it" explanations for how the world works.
Science, knowledge, and the freedom to choose our own pursuit of happiness is important for the our selves, our loved ones, and the continued advancement of humanity.
*Atheists make up less than 2% of Americans (similar in number to Mormons and Jews). 12% of "unaffiliated" people chose "nothing in particular" - although I would argue that many of them (including many of the 2.5% of Agnostics) only avoid the term "atheist" because of the negative connotations, but could at least be considered "non-theist". (http://religions.pewforum.org/affiliations)