The mass hallucination hypothesis is valid, assuming we are talking about a group of people, who may have fasted for a few days prior or hallucinated something or had a few trance sessions.
Having said this, and this is the argument Arif Ahmed made, IF you are willing to posit a SUPERnatural explanation, then the possibilities are truly endless, including a SUPERnatural mass hallucination. This point, I think, Christians don’t consider when they think that ruling out all natural leaves them with only ONE supernatural explanation.
Well, you are arguing with the Gospels here. I’ve already quoted the passages, but I will quote them again (all quotes from NASB)
Mark 6:14 And King Herod heard of it, for His name had become well known; and people were saying, “John the Baptist has risen from the dead, and that is why these miraculous powers are at work in Him.”
People were saying these things about Jesus (according to the Gospel of Mark and Matthew). Namely, that he, the person who walked about, talked, taught, ate, slept, etc… was really a risen John the Baptist.
Luke 9:18 And it happened that while He was praying alone, the disciples were with Him, and He questioned them, saying, “Who do the people say that I am?” 19 They answered and said, “John the Baptist, and others say Elijah; but others, that one of the prophets of old has risen again.”
So, this is exactly what they were saying. Jesus Christ was John the Baptist risen from the dead. And what is interesting, is that Christian apologists seldom mention this point. Its an anomaly to their worldview. But I think it’s very prominent in the Gospels. And, if anything, it makes a case for John’s resurrection. This testimony is an equivalent of finding a Pharisee document, dating to the 1st Century, stating that the disciples stole Jesus’ body. Here we have Christians acknowledging a wide held belief (people were saying…) that John rose from the dead, but they were ‘correcting’ this belief by making it known that the people were mistaken.