The very definition of belief implies there is no proof. Believers cannot quite their head around this fact in of itself, hence why the endless questions of "what is belief", questions predicated on "for those who believe in evolution", etc. It is almost as if belief is a requirement of something being factual to believers. It is almost impossible to debate someone who is not defining the very meaning of the term the same way, but that is another story...
If they just understood the simple fact they had no proof to begin with, there would be no debate at all. What this really comes down to is debating the definition of the term, which in reality is not open to any debate.
Thus your frustration, and why no proof is ever offered for such claims.
d4g