In my experience, the biggest problem theists have with atheism is the fact that atheism seems to provide no foundation for existence--especially no purpose and no moral or ethical structure.

Frankly I find most of the answers atheists give to these criticisms to be sappy rationalization, and I don't think the criticisms can be refuted. A world inhabited by God or even by Olympian super-beings is far more pleasant to imagine than one with no purpose and no morality.

Still, it is a fallacy to believe something because one does not like the consequences of the alternative.