Americans are brainwashed from a young age to think atheism = bad.
Sadly this is not just the case in America. A few years ago a work colleague, who has since gone on to enter the ministry, started a discussion on religion. Even though we had known each other for some years, this had never previously been a subject of conversation. It became obvious fairly quickly that it was assumed that I was a Christian also, so I informed him of my atheism. His reponse was that I couldn't be an atheist because he considered me to be a 'good person'.
I was a little saddened by this, and could only wonder what his religion was teaching him about the world and those inhabiting it.