From The Life and Times of Bruce Gerencser:
Shameless Christians, forgetting the Good Book condemns bearing false witness (Romans 13:9), lie about atheists and defame their character.
Why do Evangelicals act this way towards atheists? The short answer is that for Evangelicalism to have value, there must a clear distinction between good and evil; Christian and atheist. Evangelicals present themselves as pillars of moral virtue — that is until they are caught with their pants down, and then they are just like the rest of us, they say — so it necessary for atheists and other non-believers to be portrayed as people lacking morally and ethically. The Christian life is presented as the most awesome experience ever — all praise be to J-E-S-U-S — so it is necessary for atheists and other non-believers to be portrayed as having empty lives lacking meaning, purpose, and direction.