All groups have members that are jerks.
And if we were to, just for the sake of argument, say that for every ten persons on the planet one of them is a jerk, that means chances are that the bigger the religion in terms of numbers, the more jerks are going to be found adhering to that religion.
Given that Christianity constitutes about a third of the human population on the planet, I would expect to find more Christian jerks.
Which isn't to say it's only about numbers. only pointing out that even we just argued that route, it would be the case.
I think the problem is compounded by additional factors:
Christianity isn't just a populous religion, it's a powerful religion. By that I mean it has been the religion of those in power in the West for centuries, even in nations that have a separation of Church and State (such as the U.S.), it's still the case that the majority of the cultural and political elite is going to be Christian, that those in the seats of power confess Christianity as their religion, giving Christianity a cultural edge; and thus providing a larger platform for abuse of power.
Due to the nature of power politics throughout Christianity's history, there has been ample opportunity for certain theologies of power to be crafted and disseminated among the believing public--both clerical and lay. Such that the union of Christianity and Culture is a profoundly intertwined one. A Christian advocates a Christian triumphalism, whether implicitly or explicitly, because it's part of the larger cultural milieu.
When Christians were being hunted down by the powers that be, and being a Christian meant being a cultural outsider, there was no basis for such cultural triumphalist language or practice; but the moment Christianity becomes attached to the bastions of power and culture, it is necessary to see the two as somehow one and the same.
That means the outsider is now a perceived threat to the tribe, and the tribe must be defended at all costs, perhaps even preemptively and violently.
This Christian triumphalism and tribalism is endemic to the Christian enterprise in the West, and it is an arduous task to try and unweave the faith from the culture.
It also means a far larger proclivity to being a Jerk for Jesus. Jesus is the icon for the tribe, and the tribe needs defending, and that probably means acting like a jerk to those outside of the tribe.
-CryptoLutheran