I find this particular argument amusing, even astonishing, but it's the way some believers (not just religious ones, but woos of many stripes) think. I have encountered it numerous times in different contexts.
"I believe X"
"Well, okay, but believing something doesn't make it true. We can be fooled. What evidence is there to believe it?"
"But I really, really believe it!"
For some reason, really, really belief is supposed to be more convincing.
I used to be completely unable to understand how this kind of reasoning came about. Lately I suspect it has something to do with the privileged position faith is supposed to be accorded, because faith is supposed to be admirable. More faith is supposedly more admirable, and hence, more privileged. We actually are expected to find that really, really more convincing in some way, or at least to stop thinking about it!.
I originally posted thinking there was no need to refute this, but I guess the fact that I see this argument sometimes indicates that some people at least can't see just how pathetic it is. So for posterity, here's one such argument. Believing something doesn't make it true - you can be wrong, you can be deceived. Believing it more doesn't remove that.