Heh... any particular god-concept has many more people who are willing to kill and die for their belief that it's false than people who are willing to kill and die for their belief that it's true.um...
Millions of people swearing to its truth?
But it's a matter of quality, not quantity. The fact that someone (or many people) believe a claim only speaks to the truth of that claim if the people's beliefs are well-founded. And if they're well-founded, you can justify the claim with that foundation instead of the number of believers.