It's one of those you have to see it to believe it things, so there is no point in logically arguing with those who had experiences/believe. There is enough claims from individuals, organizations, hotels, vacancies, museums and hospitals to classify it as an occurring phenomena. The only way you can come to a proper conclusion on this type of phenomena is to experience it yourself, or perhaps research heavily into it. Subjective evidence does not hold weight in the scientific method, but it does call for proper investigation. You could call ghosts/spirits a "mass hysteria" or people's mind playing tricks on them but it's much deeper than that when there is multiple witnesses to several claims. You have to research it for your conclusion to hold weight.
Seeing is not believing, unless you believe the sun revolves around the earth. Experiencing a phenomena is one of the worst ways to draw conclusions about it, unless it's followed up with careful study. You have to factor out human bias and mistakes of perception, logic and memory if you want to trust in your conclusions.
In any case it is irresponsible for someone to say something like "i've experienced this thing I can't explain, therefore I can explain it, it's ghosts." If something has the property of being unexplained, that very property can not then explain it.
You are 100% correct that it classifies as a phenomena, ghost experiences transcend generation, social status, upbringing, and geographic location and each one warrants study. True investigation is the only way to draw conclusions, yet no scientific investigation, which is the most careful and fastidious investigation we have, have yielded paranormal results.
Science does not discount personal experience and hearsay, it sees these things as a pointing finger, a place to start an investigation. When science looks at ghost phenomena, we find good reasons for these fingers to be pointing. Mistakes of logic, perception and memory are at the top of the list. All humans share these inherit pitfalls. The human mind is designed not only to pick out patterns from random data, but to assign intentional agents to these patterns. People have been pointing at ghosts for a long time, and science has looked and found nothing. If this finger ever points at something new, science will happily have another look.
We can see the human factor in the pictures of ghosts that have been produced over the years. In the old days they appeared as apparitions or shadows, suspiciously close to over-exposure and other technological shortcomings of the time. With the invent of digital cameras, we now see ghosts appearing as orbs, suspiciously close to what we see when we have dust, water droplets, or other debris very close to the lens. Rather than try to identify and rule out these factors, ghost hunters jump at the chance to declare these orbs ghost energy, not realizing that the scientific context of the word 'energy' makes these statements sound meaningless to science.
The use of any kind of measuring equipment to detect ghosts is fundamentally flawed. Measuring equipment detects what it is designed to detect, whether that's light, heat, electromagnetism, or whatever. Thus it will only detect things that emit measurable amounts of those energies. For us to accept that some piece of handheld measuring equipment has a useful function in detecting a ghost, we must base our acceptance on the premise that ghosts are known to emit those types of energies in measurable amounts. If there were any truth to this, science would have discovered it long ago. Hospital operating rooms would have ghost detection equipment built in. Mortuaries and crematoriums would have ghost detection equipment at the top of their list. Search and rescue crews would use ghost detection equipment. If ghosts did exist and were detectable, you can bet that there would be huge industries behind it. I can't think of anything that would attract more venture capital dollars from Silicon Valley. However, no rigorous research has ever shown that ghosts can be reliably detected with hardware. It's easy to disbelieve me, but it's much harder to disbelieve the lack of interest from greedy corporate America.
It may be someday technology invents a tool that lets us detect ghosts, but we certainly don't have anything even close today.
It's silly to think that someone's Grandma, who couldn't even set the clock on a VCR, somehow gains the knowledge to manipulate and control sounds waves and recording equipment upon death. This is also true for anyone who died before such equipment was even invented, somehow they manage to interfere with recorders so they can announce disjointed, irrational messages to an empty basement or graveyard, like "She's in the mustard!" or "Laundry applecart tuesday". EVP's are not an example of science or investigation, they are an example of audio pareidolia, a well known and well documented phenomena. These people are not generating hypothesis and then testing them, they make no attempts to constrain factors or compare to control groups. They are simply hunting for anomalies, declaring these anomalies ghosts, and then calling it research.
The human body is not in and of itself energy, it makes and utilizes energy, and to do so it must constantly consume energy. When we die, the energy is no longer being produced, and what's left in the form of heat or caloric energy dissipates. When science says energy can not be created or destroyed, it is talking about energy that can be measured and quantified, not some imagined life energy. We know that there is no part of the brain that can be damaged without also damaging the mind. Brain trauma can change a persons tastes, personality, and even sexuality. Altering the brain can fundamentally change who you are. It is silly to think that once we damage the entire brain at death by lack of oxygen, who we are somehow stays in tact and we retain all of our cognitive abilities.