"So, do you think we have to simply go down the list in 1 Cor 15 and explain each appearance? Or do you think there might have been an earlier historical core on which the list is based on--one with less fantastic group visions and no additions like 'according to the scriptures'? "
As soon as I read it, I hastily sent off a response, admitting that I don't know, and that I usually concede that the creed is accurate, for the sake of argument. For me, it's nice to have a theory that accounts for all of the potential data- and hallucinatory experiences seem to do that. However, after thinking about it a bit- I realised that he has a point. This theory does seem kinda improbable.
Of course, I believe that no naturalistic theory for the resurrection has ever been "perfect"- that is, none have ever accounted for all of the available data at least as well as the "resurrection hypothesis". However, I don't think a naturalistic explanation needs to be exactly on par with a supernatural explanation for it to be considered, let alone favored over it. For one thing, if one is a naturalist, and finds it extremely difficult to fit God into the universe, the probability of the resurrection completely plummets, until anything is more probable than it. Also, if one has a religious experience incompatible with Christianity, they would also consider Jesus' resurrection to be very improbable.
Of course, I am not saying that we need to believe in space aliens or evil twins to remain skeptics- quite the contrary, I believe that some alternative explanations for the resurrection actually account for different pieces of information better than the resurrection hypothesis- for example, they explain the nature of the visions very well. They also explain away failed prophecies and the early disciples false scientific beliefs- but I'll save that for a later post.
All that I intend to do is show is that skeptical hypothesis aren't too implausible to believe. For one thing, apparitions are quite well known- and studied from a secular perspective (see here and here). However, I don't want to spoil too much since I plan to blog about them in the future. All that's important is that they happen more often than we'd think. We also know that visionary experiences (including group visions) were actually very common in Jesus' day- in fact, they were so common they were considered "normal". We also know that in many of these instances, the seers don't see the same thing, even though they initially think they do- which seems much more probable according to a naturalistic hypothesis than a supernatural one.
Just as a concluding thought- I want to discuss apologists that undermine the hallucination hypothesis. William Lane Craig, in spite of his ego, usually accepts that they are at least possible, stating that he feels that they are ad-hoc and improbable. Fair enough. Some other scholars, however, are much more antagonistic towards it. These scholars are most notably Gary Habermas and Mike Licona. For one thing, Habermas denies that they can even happen! Being a protestant, I wonder how he'd explain away the Marian Apparitions? Licona falls into this same trap as well. As a matter of fact, during his debate with Bart Ehrman, he once again claims ignorance as to how the Marian apparitions came to be, once again stating he hasn't seen the evidence! This is academic dishonesty, plain and simple.