I don't agree with this at all. I'm an atheist, and I'm perfectly comfortable saying so when it comes up in the conversation. I don't actively promote atheism, because proselytizing ain't our gig. However, I'm happy to share my thoughts on the matter when appropriate. For an example, see my Medium article "The Rationale for Atheism." I'd happily share more about it, except that most of the people to whom I mention I'm an atheist are atheists themselves. Problem solved.