Recently, Professor Muhammad Sven Kalisch, a convert to Islam and a scholar of Islamic theology, shocked the world by declaring that, based on his research, Muhammad probably never existed. (For the news about Kalisch, see "Muslim Academic Questions Muhammad's Existence," "Professor Hired for Outreach to Muslims Delivers a Jolt," and "Scandal Exposes Islam's Weakness.")
Let's start with the obvious. It's quite common to find Muslim apologists appealing to the most radical, anti-Christian, atheistic writings in their attacks against Christianity. For instance, this past April, as James and I debated Jalal Abualrub, Jalal said that Christians don't have any evidence that Jesus ever existed. Here he could only be basing such a claim on the hyperskeptical nonsense of some of the self-proclaimed "infidels" who write for the Secular Web. (Note: Some of the writers there are actually reasonable scholars--but not the ones who hold that Jesus was a myth.) The Jesus-myth theory has become quite popular in some circles, and Muslims seem quite happy with this (though I'm not sure why Muslims would be so delighted to hear that Jesus never existed; wouldn't this refute Islam?).
But what happens when the same radical skepticism that has been applied to Christianity for the past two centuries is applied to Islam? Kalisch gives us the answer: Muhammad probably never existed.
I have to say that I find such a conclusion to be absolutely absurd. Muhammad existed. There's no other reasonable interpretation of the evidence. Nevertheless, Kalisch's conclusion shows what can happen when Muslims suddenly become consistent in their reasoning. Islam wouldn't last five seconds against the hyperskeptical approach that is used in the West against Christianity.
To sum up the obvious: Consistency is important. If the methodology you use against Christianity would also destroy Islam, either be consistent and reject Islam or abandon your methodology. (The alternative is to defend your right to be inconsistent, as Shabir Ally did in his recent debates with James White. See here for more on this.)
Now for the less obvious. Muslim apologists don't understand how, in the long run, they're actually helping people come to Kalisch's conclusion. When I debate an Adnan Rashid or a Bassam Zawadi, they assure me that the early Muslim community was filled with liars and fools, who would not hesitate to invent false stories. They contend that Muslims passed on countless fabrications. Beyond this, we know that by the time we get to al-Bukhari, there were literally hundreds of thousands of unreliable narrations circulating in the Muslim world.
What's the obvious conclusion here? If the early Muslim scholars weren't reliable, how can we trust anything they said? If the vast majority of ahadith (well over 95%) were unreliable, how can we trust other ahadith circulating in the same community?
As I have pointed out in debates, I have more respect for the early Muslim scholars than Muslims do, which is why I accept much of what they said about Muhammad. But when Muslims have to constantly attack their own sources in order to rescue Muhammad from the embarrassing facts of history, where will such a path lead? It will lead to utter skepticism about the Muslim sources. We'll see how Islam stands up to scrutiny once Adnan and Bassam have convinced the Muslim world that their earliest scholars can't be trusted (and once young Muslims start following Sami Zaatari in showing complete contempt for Islam's greatest scholars--such as Ibn Kathir). I suspect we'll be seeing a lot more Muslims like Kalisch, defending the Muhammad-myth.