| a five minute presentation which answers your question:
http://www.youtube.com/watch?v=w4fQA9mt-Mg
and my personal response to this question earlier today:
i could say that it's because people want to legislate their religion into my country's laws. or i could say that it's for the same reason as why religious people try to 'witness' to the non believers (to get you to see the truth as i see it). i could say it's because people are always asking questions about atheists and we need to be here to answer them. i could say that i am spiritual, but not religious. i could say that i was at one time a christian, and i have studied various other religions as well, so i do have something informed to add sometimes. all those things are true, and more. however the main reason i come here is because it's the most interesting section on y!a, and i like it.
and a link to the many other questions almost exactly like this one:
http://answers.yahoo.com/search/search_result;_ylt=Aj16Q5T79gtxiCYCLELFJ0gjzKIX;_y lv=3?p=why+do+atheists+answer+questions+on+religio n+and+spirituality%3F&t=n-1012509124_q-x2U.Kxe7UyYKGoSERmzeaQAAAA%40%40&scope=&mc=&asktim e=&sc=  |