You're moving the goalposts again. Parental indoctrination of children explains the spreading of the world's religions. If I were to turn to a more detailed and specific explanation of Christianity's success, I'd have to talk about that religion's origin, which goes beyond how it spreads. So we'd have to talk about why Rome adopted that religion in the fourth century. Bart Ehrman recently published a book on that question, called The Triumph of Christianity.
The Christian message of looking out for the little guy naturally appealed to the many little guys who had been overlooked by the ancient regimes. Christianity thus Judaized the Mystery School mysticism that passed along subversive Eastern or underground, entheogenic suspicions that everyone has the same divine potential, not just the political or priestly elites. And Rome adopted that message to help tame and unite the masses as its political, military, and economic hold on its territories was crumbling.
You say a Christian can't twist the message of love into a defense of something as evil as genocide. But don't you think the Inquisitors professed to love the soul of the "witch" he tortured? It's love of the invisible, immortal soul that matters to Christians, not love just of the material person. The material form can therefore be sacrificed for higher, spiritual purposes. I believe Jesus, the founder of this religion, provided the paradigm with his death on the cross. So it's the ends justifying the means, the core of Machiavellianism.
You're a Catholic, so you say only Catholics are Christian. But do you really want to say that Protestants aren't Christians, that they're heretics? Remember, the question isn't whether Christianity can be defined. It's whether the religion can be defined in a way that isn't nakedly political and anti-spiritual.
The Catholic's reliance on the dubious passage about Jesus's handing over the keys to Peter isn't a spiritual matter that speaks to a dignified core of the religion. Catholicizing books like Luke-Acts were selected over Gnostic ones to consolidate the power of the church as an earthly institution as the centuries wore on and the prophesied end of the world didn't materialize. Again, that's a political matter, and politicians excel at spinning matters in their favour. There are plenty of politicians outside of Christianity, so it doesn't seem wise to define your religion in such political terms.
