
 > A Christian friend of mine once reasoned that if we were never
 > created, we could not exists. Therefore we were created, and
 > therefore there exists a Creator.

I hesitate to comment on the validity of this, because I do not know
what your friend meant by it. If he meant that whatever exists must
have been created, then he is open to the obvious retort that God
exists, and so God must have been created.

Perhaps your friend meant that we exist now but that there was a
time when we did not exist, and therefore something other than
ourselves must have brought us into existence. This seems plausible,
but an atheist might reply, "So my parents engendered me. So what?"
Here your friend would have to explain why an infinite regress of
causes is not a satisfactory explanation. He would have some support
from philosophers who are not ordinarily considered religious (Ayn
Rand, and some others who are in the tradition of Aristotle). Having
argued for a First Cause, he would have to bridge the gap between
said entity and the God of Abraham. If he merely asserts that the
things we observe are ultimately dependent on things radically
unlike them, few physicists would disagree.