The OP question is a very valid one, and one that I have asked myself many times: on what does anybody base his or her faith?
I am pretty sure that if I had been born in a Muslim or Hindu country that I would have been a Muslim or Hindu.
As it happened, I was born in a Christian household, with rigid protestant parents. The Catholic Church was the Scarlet Woman, the Antichrist! Yet, as I related in my own thread a while back, I did have many personal expereineces of interaction with the Divine, which have cemented my faith.
FMF relates about a turning point that he had which turned him against, and away from, Christianity. My own turning point (if I can call it that, or rather growth point) occured when my son became a Buddhist, and I asked myself: "This child of my loins is not an idiot. What does he know that I don't? who am I to say that he doesn't see something that I don't?"
So my journey has been in putting my Christian beliefs (which I have not shed) into a different framework, and seeing some teachings in the NT in a fundamentally different light (e.g. the whole eternal punishment thing, the 6000 year old universe, the universality of God's love, etc) . It is a simple thing for me to accept atheists as just fellow travellers on this journey, to see compassion and mercy as the ultimate virtues, rather than BEING RIGHT and having sole insight into TRUTH.
On what do I base my faith? Firstly, on the personal experiences that I have had that there IS the DIVINE, and that the purpose of this DIVINE is to be united with me, and then me with everything around me.
But secondly, that this is the only thing that makes sense to me. Fundamental Christianity forced me to be internally inconsistent and a moral fraud, in that I knew that in my heart of hearts I did not really believe what I said I believed.
But I did not jettison it as FMF did, rather included it in a far bigger picture.