One of the greatest benefits of being an Atheist is the value it places on this life. Since Atheists do not believe in any existence after death, such as reincarnation or some kind of afterlife, this time on Earth is all we have. For me, this greatly increases the motivation to make the best use of the time we have while we are alive.
There are many different dangers of religious thought, but one of the greatest that I see is the idea that this world and our lives are just some kind of opening act to the real show we are told takes place after we die. Of course, theists take this belief to heart, leading to different consequences for themselves and others.
Some theists respond to this belief by living their life in some kind of preparation for what they are told is the next. They spend a lot of time reading religious texts, praying, or ministering to others. There is also a portion of these people who seem to spend more time thinking about the afterlife than they do about this one. My point in saying this is not that we should pass some laws to forbid them from doing these things. I believe in freedom and the right of people to live their lives as they wish. My point is that I wonder how much farther ahead we would be in fields of science that actually produce demonstrably beneficial results if people were to spend their time furthering such progress.
Other theists are affected by religious beliefs in a way more serious than the one just described. These are theists who, for one reason or another, are not content with their lives. Perhaps they have a job they hate or are continuing relationships which are harmful to them, such as people told that it is sinful to divorce and will not leave abusive relationships. Belief in an eternal afterlife filled with pleasure seems to make these people content to take a backseat in their present life. They are, in essence, waiting for their own deaths, which will bring about what they think is the most important life. To me, this breeds complacency and can steal a person's life away from them. I believe that if more people disbelieved in an afterlife, they would be more motivated to make changes in their life leading to happier and more productive lives. I make efforts to live my life this way and work to make each day important, meaningful, and purposeful. I am an Atheist with a good and meaningful purpose driven life.
Before finishing, it is critical the reader understands that in no way am I insinuating that somehow all theists do not live life to the fullest. I have seen many theists who do make the most of their lives each day. However, I have also been a witness to many people who do not. In this way, I see religious beliefs regarding the afterlife as being potentially harmful to people.