Why do atheists proselytize? Why do they try to convert others to their faith? For many of the same reasons every other faith proselytizes. Community, self-affirmation, even power are among the reasons. Atheists want people to believe like they do so that they can live in a society where man's own limited reason is their god, where government and policy is inspired by their god, where social norms are swayed by their god.
This is a glimpse of one section of the real War. Throughout the history of mankind battles for physical power have come and gone, but the larger war for the hearts and minds of God's children has continued unabated. The most important battle is not over whether we live or die, but over who and what we will believe in. You cannot help but serve truth or error.