I'm not someone who tries to spread atheism or non-belief but I have a couple questions for the board while we're on the subject.
Is it wrong for a believer to try to spread christianity? Is it wrong for an atheist to try and spread atheism? (both using non-violent means)
The short answer is yes to both questions.
Those of us who try to 'spread Christianity' too often do so by making God a tyrant and the Christ a most unappealing figure. And too often the end product is an empty religion that goes through the motions but produces few of the benefits and crumbles under adversity. We were never commanded to spread Christianity. We are commanded to spread the Gospel, that is God made promises throughout human history, He was with us to fulfill those promises, and He loves us. Those He calls to teach can get into the finer points. Our job is to make the introduction. He takes it from there to change hearts and spread Christianity. Christianity, boiled down to its barest essentials, is not a religion. It is a relationship with the living God.
To try to 'spread Atheism' requires taking faith that brings billions of people joy, hope, comfort, and peace and replacing it with emptiness. When you compare societies that are predominantly Christian with societies that are predominantly Atheist, it should be apparent which produces the most compassion, good, and aesthetically pleasing way of life.