"What can be asserted without evidence can also be dismissed without evidence."
- Christopher Hitchens
Although this quote (known as Hitchens's razor) is from an avowed atheist and was used to express disdain for the beliefs of theists such as myself, it is nonetheless correct. Indeed, I have found it quite useful in my debates with atheists themselves. It turns out they have many wild beliefs that they assert without evidence.
For instance, the other day I presented an atheist with the cosmological argument, and he responded by citing a paper Stephen Hawking wrote at the end of his life explaining how the universe could have arisen spontaneously. When I followed his link and read Hawking's quotes about the paper, I noticed that claim was predicated on the belief that there are multiple universes (the so-called "multiverse" concept).
I happen to know there is no evidence whatsoever that multiple universes exist, so I responded by simply quoting Hitchens's razor. As I said, it is quite useful!