According to Audacious Epigone. atheists are most likely to live alone.
This is not surprising. Atheists are less desirable sexual partners. I observed this once when I was living in Washington, DC, and I wandered by an atheist convention happening on the mall. The atheist were predominately male, and significantly uglier than average.
This is because ugly people become social outcasts, and social outcasts are more likely to be attracted to outcast movements like atheism, libertarianism, communism, etc.
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Jay Fink writes:
If you are attractive and have a good social life you will generally not be interested in out of the mainstream groups or ideas. Why buck the status quo when it's working in your interests?
Exactly my point!