Why people become atheists?

I am an atheist because I don't believe in deities and the word atheist describes this state of disbelief. I don't believe in deities because no argument or evidence presented to me in support of their existence has been convincing.

1. Biology adequately describes life and emotions without appealing to mystical invisible dieties

2. Astronomy adequately describes the formation of stars/planets/universe/etc without appealing to mystical invisible dieties

3. Geology adequately describes the evolution of the Earth, land formations, etc without appealing to mystical invisible dieties

4. Psychology describes the human psyche better than appealing to mystical invisible dieties

5. Appealing to mystical invisible dieties is an appeal to ignorance

6. There's no physical evidence for the existence of mystical invisible dieties

7. A myriad of mystical invisible dieties have been posited by emphatically superstitious societies and have been proven to be products of overly active imaginations (today's religion is tomorrow's myth) and ignorance.

8. Believing in mystical invisible dieties seems to become quite absurd when those who posit the mystical invisible dieties begin explaining why and how they exist in the face of contradictory physical evidence.

9. As scientific knowledge increases, the role of the mystical invisible dieties oddly gets pushed further and further back.

10. Mystical invisible dieties are mystical invisible dieties (ie can never be found by empirical methods)

That should be enough to get you started.