We are ignoring it because honestly it's not as big of a problem as you are making it out to be. I know people like that too but they are in the minority. And just because someone is mentally ill, that doesn't discredit their entire experience. Firstly, mental illness comes in various levels and types. Most mental illnesses do not affect ability to clearly discern reality from illusion. You are brushing a large issue under the rug by lumping a huge group of people together and judging them by the hairs of only a few of them. Secondly, lets assume someone has a mental illness where they can't discern reality from illusion. If this person observes a paranormal occurence together with another person, both confirm that they see the same thing, they observe the circumstances and come to the conclusion that it is not the wind, do you really discredit it just because the experience was had by someone with a mental illness? Doing so would be irrational and disrespectful.
If you cut the attitude for a moment and look at what we are actually talking about, many of us are talking about events experienced by several people either all at once or within short timeframes of each other. Events that took different forms: physical, auditory, visual.
If I started hearing voices right this moment I would check with other individuals present to see if they hear them. If they don't, I will assume the problem lies with me unless I see further signs. That's what most people do. Most of us will assume natural causes before we assume ghosts because you know what? Some of these visitors are cool, others are very much unwanted and we would rather not believe they are real. But you are assuming that we don't. You're assuming we'd tell someone who only hears voices to see a priest before they see a therapist.
I can honestly tell you I wouldn't. I have spoken to people who have experienced a combination of hearing voices, losing control of their own body, having heavy objects be moved by noone, and more. I suggested therapist firsthand and the paranormal secondary - and that was ONLY because of the unexplainable movement of actual objects (confirmed by other people present). These people have since reached out to get help and are doing better. Movement of actual objects still remains unexplainable.
Look, I don't care if you don't believe in ghosts. I respect that, as I have said, because most people wouldn't do that without seeing convincing evidence with their own eyes or hearing it from someone they trust. But cut the condescending attitude. In fact, cut the condescending attitude in general. It brings down the general mood of any thread it is used in