Ooh, I see what you did there: "I define god as "good" and / or "mystery", therefore someone who doesn't believe in "god" doesn't believe in "good" or "mystery"".
Terribly clever.
Except that atheists DO experience mysteries, life and goodness. We simply don't believe in the existence of anthropomorphised deities.
You're forgetting that the subject under scope here is a religion or belief system. What does someone reffer to when they say, " thank God for this or for that?" They are also saying "thank goodness for something that has occurred," Correct? Look closer please. They're thanking the mysterious patterns of goodness and fortune (i.e. over their heads) that worked in their favor- that enrich their Life.
They develope a spiritual and emotional connection to it. If they understood it then they could control it with knowledge and science. But, there is no knowledge yet for those patterns, therefore belief and faith is used to help bring it into their Life by the objective laws of cause and effect. It's connected with their religion or belief system. It doesn't take a rocket scientist to figure this out. Beliefs and faiths will seek to express their self in someone's own Life and experience. It always does.
Beliefs affect the World and everyone in it. One of the downsides of atheism is that the position prevents many people from acknowledging the affects and creations caused from the beliefs in God, the gods or the Divine. In fact, it can completely blind side them into not using their own capacity to believe in things and therefore enhance their own Life. So, what happens when someone realizes that the very language they think and speak with was also aided by faiths and beliefs?
Ridiculing many of our ancestors faiths and beliefs is the equivelant of shouting to everyone that english is for idiots, in english. Think about it...IMO