As I understand them, psi experimentation could be viewed as an altruistic exercise on the part of the experimenters, all of whom hope to explain a phenomenon that most people cannot directly witness themselves. It is the altruistic nature of this exercise that causes parapsychologists to work long hours on these subjects despite poor funding and heaps of scorn from other professionals, negative publicity, and the general public. It is altruism that causes these men and women to alter their experiments frequently, to answer questions or criticisms by skeptics. It doesn't even matter how well-grounded an objection is, they'll cater to the whims of people who haven't the slightest notion how experiments are conducted or how the data is interpreted or indeed what inadequate or fraudulent data looks like. If this weren't true, you wouldn't see Julie Bieschel going beyond double-blind experiments to triple-blind, quadruple-blind and even quintuple-blind. You wouldn't have Rupert Sheldrake using dogs as subjects, because that completely eliminates many objections about the motives of human subjects. You wouldn't have researchers discarding NDE data unless the subject was clinically dead, had a flat EEG, and was congenitally blind (as Ring did in one study.)
All of this, all of these ridiculous extremes, these cost the literature tremendous quantities of perfectly good data. But why is all of this valuable data sacrificed? Altruism. The people who do it are trying to explain a difficult thing to people who do not understand it and have no idea what it should look like. So they are patient. They know the objections don't always make sense, but they cooperate anyway because they know that they will be able to demonstrate something despite limitations that would have scientists in other fields crying "Foul!"
It can be quite frustrating, but on the other hand it is also true that bending to these often silly requests has its own challenge. "Can I show it in this way?" The parapsychologist might ask himself, and then with some pleasure discover that it can be done, like progressively increasing the difficulty of a video game. At a certain point however, the process no longer serves the original goal. It is possible to over train and in so doing lose the time for legitimate appropriate research that was instead spent distracted, working on ever-higher levels of difficulty that never connected very well with one's original research interests.
It seems to me that as long as experimental research is conducted by people who are genuinely interested in it and who think it is the most legitimate method of answering certain questions, it is a legitimate endeavor. However, when that same research is directed by the arbitrary and uninformed criticisms of people who are fanatically attached to the desire of curtailing, stopping, interfering with, or in some other way harming the research, one might expect that work to run aground from time to time.
It may be that psi research threatens other fields. Frankly, I think it not only does "threaten" other fields, but the facts behind the research, the reality it is based on, already makes a mockery of several basic principles in a variety of sciences. Reincarnation, spirits, telepathy, PK, spirit guides, all of these and other related phenomena show that there is much more than modern physics, medicine, or religion has seriously contemplated. For this, research into psi is dangerous because once these things are demonstrated, many ideas accepted for a mere two centuries or so, must fall. Why, with this opposition, do others persist? Because it is a part of nature to explain when asked a question, and to want to tell the truth if one knows it--particularly if others don't. Again, altruism.