In my experience meditation can be dangerous in a few situations.
Becoming very attached to the bliss/euphoria in certain states of meditation. Then one day the bliss goes away, or sometimes you don't have a blissful meditation, and well most of us know what happens when we don't get what we want.
Taking experiences too literally, or putting too much stock in them, many experiences can/will/do happen during meditation, and during waking/sleeping hours when someone meditates alot.
I think in deeper levels of meditation, and when someone practices for many hours a day, this is where we begin to need guidance, and advice from an experienced teacher, because in deeper states of meditation we CAN do ourselves real harm. Deep meditation allows for deep rooted change of our psyches, including our sense of self, where an inexperienced person may see devas/demons and gods or hear voices, another more experienced person may understand how our deluded perceptions creates these illusions, and continue into there meditations safely.
There is also an afterglow after engaging in daily deep meditations, where the line between meditation and waking life merge, and these experiences can creep into daily experience. For someone without good and wise guidance it's possible to get into alot of trouble here also. Think of meditation at an extensive retreat without any guidance or experience what-so-ever. Duh.
Can daily 5-10 minute meditations, or simple mindfulness throughout the day cause people harm without a teacher? Probably not. That wasn't the question though.
Also to the OP, I think I glanced your other post, and while some experiences may be genuine, I would say 99% are mental issues, which are caused by our minds naturally tendency to identify things as solid and existing entities, in reality it's all in the way we perceive what we experience. In Buddhist literature there is a relevant quote.
A man walks into a dark room and sees something coiled on the floor. In a gut reaction he mistakes a coiled rope to be a coiled snake. When he collects his frantic energy enough to turn on the lights and the darkness vanishes, what is illuminated is the true nature of the object.