Some time ago, I got in a brief conversation with someone on a friend's Facebook page. To make a long (and painful) story short, it was essentially a discussion on whether or not Christ taught national healthcare. I argued that all of Christ's acts of charity were directly tied to His deity and that acts of charity were done by choice and through the church as a body. The other person argued that Christ approved of actions done by a sympathetic government. I then asked him to provide scripture to back up his case (I had done so for my own). It was then that the conversation took a turn, and the man began to argue that you didn't have to cite scripture, and that in the end it didn't matter what anyone believed, since with religion everyone was right.
I bring this up as only one example wherein conflicting presuppositions are brought into play, though unknowingly by the person presenting them. These conflicting presuppositions often boil down to something similar to this scheme:
Presupposition A: We have no way of truly knowing what Jesus taught.
Presupposition B: Jesus was a great teacher of morality and ethics, and taught X, Y, and Z.
Presupposition A is often introduced with a series of doubtful statements. One example is: "We have no way of knowing what the original Bible says because of the textual variances." Another example is: "There were so many books in the early church that we don't know which ones really depict what Jesus said." Another might be: "The books about Jesus were written later, so they aren't an accurate depiction of what His teachings or actions were." In all these scenarios, doubt is cast upon the assurance of knowing who Christ was, what He did, and what He said.
Presupposition B is often introduced to promote various forms of the social gospel or "religionless" Christianity. It essentially takes the morality and ethics of Christ's teaching sans His deity, and promotes it as a code of works for society as a whole to live by. People may deny Christ's deity or any dependence upon faith in Him, but will assure the listener something along the lines of: "I believe Christ to be a good moral teacher." Or they might proceed to go into a series of such moral teachings (providing for the poor, helping the sick, etc.) which they believe Christ taught to His followers and the general world population to follow.
Note, however, the fallacy in this mindset: they assert that A and B are both true, yet B is entirely dependent upon A being false. In order for us to believe that Christ taught morals and ethics, we have to know what those morals and ethics were; in order for us to know what those morals and ethics were, we have to know what Christ said. Therefore, as stated before, in order for B to be true, then A must be false. If A is true, then B is false. A and B cannot coexist without a complete contradiction.
Initially, I was going to write this off as being selective about your sources with a circular reasoning - that is, you choose what you want to use because it promotes your case, and throw out what you don't want because it doesn't promote your case. However, I realized this is even worse than that: you're denying the validity of a source, then saying that same source proves your point. In the end you are simply left with a fallacious position due to its inherently contradictory nature.
The fact is, our main source of knowing Christ is from scripture. Scripture teaches us what Christ taught and did. We cannot pick and choose what we want to believe Christ said or did any more we could do so for other historical figures. And among what Christ said and did was confirmation of His deity and the power given Him by the Father to judge the souls of men. We can deny this in our hearts, but we cannot hide from it. I urge everyone who reads this post to consider these words, and to meditate on what Christ says in scripture, and to know that He has been sent to call men to repentance and to prepare them for that day when all men will be judged through Christ Jesus. God bless.