First of all, we need to define what a “ghost” is. If we do not know exactly what we are talking about, then we will not be speaking precisely, and I want to speak precisely. A ghost is a person who had died, but whose soul/spirit is left behind on the earth and interacts in some way with physical reality. In some sense this person is still “here” on the earth. Two questions come to mind: What does the Bible say about ghosts, and what is the evidence, outside of the Bible, for ghosts?
First of all, the Bible describes what happens to human persons when they die. They go to a “place” that is variously called Hades, Sheol, Abaddon and/or Paradise. This is, apparently, a waiting place before final judgment. There are a moderate number of passages that imply this. I will not make that scriptural argument here, but invite you to look up passages which use these English words in translation. Here is the bottom line, there is NO biblical EVIDENCE that human souls are left behind here on the earth when we die. The biblical evidence is that we go to Hades. There is one possible exception to this statement that there is no evidence for ghosts, and that is the very interesting story of Saul and the witch of Endor. This story is found in 1 Samuel 28:3-25. In this account, the witch (more accurately a medium) is asked by Saul to consult the dead Samuel on a question about a potential battle. The woman is clearly a fraud, but when she consults Samuel, to her shock and amazement, he responds, but not in a positive way. This could be used as evidence for ghosts, except that it does not fit the definition of ghosts given above. The story implies that Saul is speaking from what we would call Hades (Saul would have called it Sheol). The Bible implies life after death, but that this “life” does not hang out on the physical earth, but in an undefined other place known as Hades. By the way, there are biblical accounts of people who believed in ghosts, such as the apostles when they saw Jesus walking on water, but this is evidence of superstition, not of the reality of ghosts.
So, my conclusion is that the Bible does not support the existence of ghosts. I would point out, however, that there is no passage in the Bible which definitively and finally proves that ghosts are not real. In other words, the biblical evidence points away from ghosts, but one can argue that it is not absolute proof against ghosts.
Which brings me to the second question (and gets me close to answering your question). If the Bible points pretty strongly away from the idea of ghosts, but seems to at least discourage such a belief, is there any evidence from outside the Bible for the existence of ghosts? Actually, the group I am president of–the Apologetics Research Society–did an entire conference on the question of the paranormal, which definitely included the question of ghosts. (the proceedings of this conference are available at www.ipibooks.com) We did the conference on the Queen Mary, and it included a “ghost hunt” by a professional ghost hunter! Of course, we found no evidence of ghosts on the ship! Here is my conclusion. There is zero reproducible, reliable physical evidence for the existence of ghosts. Period. End of story. ALL of the supposed “evidence” for ghosts is anecdotal. In other words, the only evidence for ghosts is from personal testimonies. This is not scientific evidence!
At our conference we heard from two or three people who are Christians who reported their own anecdotal evidence for ghosts. This included a well-known evangelist. When you listen to their stories it can even sound convincing at the times. Is this proof of ghosts? I will say that I remain very skeptical of such anecdotal evidence. However, even as a very skeptical scientist, and as a Christian with no biblical evidence, I want to be humble and say that I cannot absolutely disprove the existence of ghosts. I am highly skeptical but am unwilling to fully close down the possibility.
So, is it “stupid” to believe in ghosts? I think that some people believe in ghosts for stupid reasons, as they are very gullible. Some people will believe almost anything and are not even influenced by evidence. I do not like the disrespectful word “stupid,” but the word may apply in some cases. However, I am not willing to carte blanche label all people who believe in ghosts as “stupid.” Some people whose intelligence and reasonableness I cannot discount believe in ghosts because of their own anecdotal experience and I am not willing to call such people stupid.