How do we know what's hot? How do we know what's red? When I feel heat, or when I see the color red, how do I know I am experiencing the same sensations as when you feel heat, or when you see red?
The fact of the matter is: I don't, and I can't. I have no way of knowing how your experience of these sensations compares to my own. The question is, then, how can any two people ever confer on what is hot, or what is red? How can we agree? How can we established, objectively, what is hot and what is red?
The solution to this lies within how we develop the notions of "hot" and "red" in the first place. We learn from observation and explicit teaching from others around us. We see an object, it has a color, others identify it as "red". I see a fire, I feel a sensation, others identify it as "hot". Through the course of my growth, I develop a mental database of objects that have these qualities and, from that, I derive a concept of "redness" and "hotness" independent of the objects that possess those qualities. And everyone else does the same.
Because of this, the actual manner I experience those sensations is irrelevant. You know what I'm talking about because our concepts of these sensations are based upon the same (or similar) physical reference points. So when I say that something is "hot" what I'm really saying is that this object produces a sensation within me similar or identical the sensation produced by all other objects I have experienced as "hot" (stoves, fires, radiators, etc) and since you have also experienced these objects, you can relate.
However, remove those common physical reference points and the word becomes meaningless, because there is no way to relate.
With this established, we move onto more abstract sensations. Love, for example. Love is often brought up in religious conversations as an example of something we know exists, yet have trouble proving or defining. It is not true to say, though, that love is not attached to anything physical. Take the following example:
You see two pairs of people in a park. One pair are leisurely walking down a path, holding hands. They stop to admire a couple of kids playing. They stop, look longingly into each other's eyes, and kiss.
One member of the other pair is wearing a ski-mask and chasing the other whistly wielding a knife. After catching the other, demands money, then runs off.
Now, if I were to ask you which pair is most likely "in love" I think (and hope) we can all conclude the same. So, despite our inability to conclusively define or articulate what love is or how it is expressed, there can be no doubt that there are physical reference points we can use to make decisions regarding it. If such were not the case, then we would not be able to even guess as to which pair was in love.
Thus, our conception of "love" is built up in the same manner as our conceptions of "hot" and "red". Love is more difficult to articulate because the physical reference points are wide and varied and not definitive. If I see a fire, I have a high level of assurance that it will be hot. If I see two people kiss, I have some reason to believe, though not necessarily conclude, that they are in love.
Even among such "concrete" concepts as "hot" and "red" there are threshold areas where people may disagree. Is something "hot" or just "warm"? Is this paint "red" or "red-orange"? These grey areas do not refute the fact that these concepts have physical reference points and those points are necessary for us to understand one another.
So what is the point of all of this? The point is in how this relates to theists "experiencing" the Holy spirit. The problem is that there lacks a physical reference point. As shown, without a physical reference point, there is little you can conclude about this sensation. You can't know that you are experiencing the same sensation as other people when they say they experience the Holy Spirit. You can't know that the source of those sensations is the same. And you can't know that the source of the sensation is accurately described in whatever dogma or interpretation of dogma you choose to believe.
This undeniable fact doesn't stop theists from claiming that millions of people's alleged experiences are somehow evidence to a single entity. This is called collusion, and it is a circumvention of standard methods.
Collusion is a term I hear rather often in my field of expertise (IT security). Basically, in order to keep a single person from having too much power, there is a management control called separation of duties, where significant tasks cannot be completed by a single person. It requires cooperation. Collusion is essentially cooperation, specifically cooperation to circumvent the controls put in place. A more accurate term would be conspiracy.
Requiring two people to unlock a missile control code on a submarine is an example of separation of duties. One person cannot decide to simply launch a missile upon a whim. The idea here is that it is less likely that two people will act with malicious intent, or otherwise accidentally. However, two people certainly can conspire to do so, and that is collusion.
And that is what is happening here. Based on some sensation without a known physical reference point, no truth or fact is able to be learned. We can't know exactly what is the source. We can't know that two people are experiencing the same sensation. We can't know that the source of those sensations is the same for two people and we can't know that the source is accurately described in some dogma. No truth should be able to be derived from the merely "experiencing the Holy Spirit". However, theists tacitly conspire to circumvent this road block. They simply agree that the source of these sensations is not only the same, but is described accurately in some ancient text. They have no way of verifying this, yet, for the purposes of advancing and generating the appearance of legitimacy, they simply agree that it is the same, creating the illusion of some truth or fact.
But, like collusion, this is dishonest and counter to how things should operate. If there is a box, and we have no way of knowing what's inside, just because two people decide to agree on what they think is in the box doesn't magically make that thing appear within the box and, even if it did, we would still have no way of knowing.
So, you say you "experience" the Holy Spirit? Good for you, but you have no way of knowing.