Coming Out...

It seems extraordinary that in this supposedly secular and enlightened society, it should be so difficult to make the decision to declare myself an atheist. If, for instance, I tick a box on an application form to say that I am a Christian or a Muslim no one is surprised, but if instead I add that simple word "Atheist", it immediately seems to ring alarm bells - Radical - Freethinker - Independent - Nonconformist - Dangerous - Fanatical - Won't fit...
And yet I am no extremist, and honestly believe I lead a moral life, living by the creed that I should not do to anyone else what I would not like them to do to me similar circumstances. I am comforted by the knowledge that this is our one life, and that I need fear neither the wrath of a vindictive God, nor the futility of eternal immaterial "paradise".
Why do people feel so threatened by sincere discrete atheists?