[ nitpick ] Schweitzer published Quest of the Historical Jesus in 1906. He went to Africa as a doctor, rather than as a pastor as he initially intended, in 1913. On being interned and brought back to France as a foreign national in 1917 (his hospital was in French Equatorial Africa), he resumed preaching in Europe following WWI, returning to Africa in 1924. While he eventually left the church, his attitude toward both Lutheran doctrine and Christianity, in general, displayed a certain ambivalence throughout the rest of his life, appearing atheistic in some contexts and devout in others.
[ /excessively long nitpick ]
You might want to go look up the Jesus Seminar at Rutgers or the Westar Institute Jesus Seminar to see a bunch of people who really take this seriously.
I think the Jesus Seminar people are doing interesting work, but I think that they have seriously stretched the boundaries of credibility. The good that they do is to collect a broad group of scholars from widely divergent fields in a forum which allows them to criticize each others’ conclusions in an interdisciplinary way. This removes some of the complaints that some “religious guy” with a preconceived notion of what to find has missed the obvious (non-religious) objections to his “faith based interpretation” of the stories of Jesus.
Unfortunately, I find the consensus approach leaves me less than impressed. In one respect, I appreciate their approach. The best lecturer that I had on exigetical scholarship, when I was in school, followed a method somewhat similar to their approach. Taking any given passage, he ran down all the parallel passages, identified as much as possible of the cultural significance found in the language of each of the passages, tracked down historical information surrounding the original passage and all the parallels, drew further parallels between the historic events, considered the earliest commentaries that could be found regarding the passage and determined their historical context, and moved on to see if he could exhaust us with the further etymology of each word in the text.
However, when all that has been done to examine each word, one still comes back to a document that was written by one (usually) human in one place and time and we simply cannot know that we have identified the historical accuracy of any phrase. While I would not be surprised to discover that some of the texts have been “enhanced” by later authors, I find most claims for the massive re-writing of those texts by the early Christians to be a bit far-fetched. For one thing, we have multiple translations of those works into Syraic, Coptic, and other languages that are, themelves, quite old and which agree, both with the Greek and with each other. (Most of these translations are held by people bearing religious animosity toward each other, so the likelihood of a conspiracy diminishes–although, of course ::: sigh ::: it never disappears.)
The Jesus Seminar tries to side-step that problem by voting on the “likelihood” of any phrase or event based on their conception of what was likely. Each phrase is rated as “certain” through stages of “likely/unlikely” to “certainly not.” I am afraid that I am not willing to grant these scholars (and they are scholars) that much credibility that they can actually parse out the historical from the legendary on a phrase-by-phrase basis. (For one thing, just as with the caricature of the “religious scholar” who is blinded by his beliefs, the majority of the Jesus Seminar members also bring their own prejudices to the forum–it is simply harder to identify their collective prejudices.)
So where do I stand? I suspect that we cannot ever truly identify the historical Jesus. I am not out in the realm of Rudolph Bultmann* who came to believe that nothing in the gospels ever had to happen because both the reality and the significance are entailed solely in the belief. However, I do not think that we have enough evidence to identify the actual historical events with anything approaching the certitude of either a biblical literalist on one side or a member of the Jesus Seminar on the other.
As to separating the “Christ of Faith” from the “Historical Jesus,” if the latter is, ultimately, not knowable, how does one even attempt to separate them? From that perspective, I guess that they are not separable. On the other hand, I’d have to see specific statements from Witherington to know whether I would support him, choose to respectfully differ, or simply consider him a loon.
*Bultmann was an early questor after the historical Jesus who decided that we could never discover the Truth, and began to explore whether that Truth was a matter that required certifiable knowledge or whether the belief that sustained the stories was actually more important.