Politics certainly accounts for much violence done in the name of religion, but the atrocities perpetrated by monotheists (especially Christians and Muslims) are overdetermined because they have religious as well as political motives.

There's little tolerance baked into Christianity. Sure, Christians are supposed to love their enemies, but they also think their organization is the only way of escaping eternal punishment in hell. So the end often justifies the means for them. Monotheism is inherently totalitarian. (For obvious historical reasons, Judaism is an exception here: Jews lived out the totalitarian implications of monotheism mainly in their scriptural fantasies.)

Most scholars who care to examine the issue of Jesus's historicity in depth are Christian, so they have a conflict of interest.

Also, the historical question of whether someone in particular actually lived in the ancient past is different from the philosophical version of that question. Historians' epistemic standards aren't as absolute. They might compromise just for the sake of carrying on the discussion, whereas the philosopher wants the truth regardless of whether the truth is subversive. In short, philosophers are likely to be more subversive than historians.