Pulling back up the original question of what causes such great diversity among Christian believers, the simple answer is money-resources conflict, religion as we imagine it in our hearts and politics over what our institutional structure should be. Further, think of all Christian brethren on three levels: an individual level, a local corporate level and a universal cultural level.
As individuals, we are influenced by nature and nurture. We are born with a particular gift mix, mental abilities, and inclinations toward temperament. Additionally, we are selfishly inclined and this selfishness is bundled in three areas, our bodies, our hearts and our minds. We have fallen natures, but it is important to recognize this nature has three parts.
On a corporate level, whenever we build communities of believers, we not only bring our individual baggage but we also encounter a corporate structure inherited across centuries of development. Regardless of our current stream, this structure includes decision-making by others reaching us through time. The natural, social construct we call "church" dictates to the individuals how to behave directly through "objective" teaching and indirectly through "subjective" teaching. We call this tradition. Another factor of seeing differently is that a relatively short stretch of time causes people who know an older set of mores to mix with folks inculcated amid a set of altered cultural norms. This has never been truer than today when cultural change is more rapid than ever.
From the broadest cultural view, the Body of Christ experiences some twists in thinking as well. The church develops concurrently with the culture in which it is based, interacts and can be pulled in. There are plenty of examples of churches taking cultural stands that were wrong. Southern pastors of the early-mid 1800's "preached" in favor of slavery. Many churches in Nazi Germany supported the fascist regime; the Crusades and the Inquisition were cultural mandates of the church itself.
This is becoming long, but you can see that the ground of our hearts is rich for disagreement and the opportunities for us to see things differently as a function of our socialization are many. When I confront someone whose whole social experience culturally and historically is different from me, and he disagrees with my take on Scripture, how do I respond? Is it not understandable that differences will be there? If we realized and embraced that what we are being asked by God is to establish among ourselves deeply loving relationships built on the social order of heaven, we would approach strangers who profess Christ differently. What if we understood Christianity as a spiritual state that is wholly different from our identities shaped of the earth? What if we sought to simply love others inspired by the Spirit of Christ within our hearts?
Jas 3:13 t0 Jas 4:1
Who among you is wise and understanding? Let him show by his good behavior his deeds in the gentleness of wisdom. But if you have bitter jealousy and selfish ambition in your heart, do not be arrogant and so lie against the truth. This wisdom is not that which comes down from above, but is earthly, natural, demonic. For where jealousy and selfish ambition exist, there is disorder and every evil thing. But the wisdom from above is first pure, then peaceable, gentle, reasonable, full of mercy and good fruits, unwavering, without hypocrisy. What is the source of quarrels and conflicts among you? Is not the source your pleasures that wage war in your members?