SurvivalAfterDeath.org has published some fascinating essays from the history of psychical research and parapsychology. Here is an excerpt from an essay by Hans Enysenck and Carl Sargent (emphasis added by me):
Finally, scientists have queried the research methods and statistics of parapsychologists - in isolated skirmishes. This seems to be a symptom of their concern rather than part of it. The statistical issues were settled many years ago, and whilst some researchers occasionally make slips, parapsychologists generally are extremely careful and even over-conservative in their evaluations of experiments. Similar comments would apply to methods of experimenting: the average standard is better than it was, say, 30 years ago, and a pinnacle of achievement like Schmidt's work has produced many laudatory comments from parapsylchologists and sceptics alike. Anyone trying to mount a comprehensive critical attack on parapsychology from a statistical viewpoint would be doomed to failure (no-one has tried for the last 30 years). An attack based solely on criticism of research methods could not survive without extensive appeal to fraud (which, as we've seen, is all unscientific and corrupting argument - like heroin once get the taste for it you can't stop).
This exhausts all the rational sceptical arguments which are brought to bear on parapsychology. However, it is clear that a purely rational perspective will not suffice to explain scientific attitudes. What makes John Taylor utter emotive (and amusing) phrases like 'ESP is dead'? What made one colleague of Sargent's say to him, after a discussion of his, and other researcher's, Ganzfeld-ESP work, 'The results you presented would convince me of anything else, but this: I just cannot believe it and I don't know why'? A story told to us by Dr Bernard Dixon, an ex-editor of New Scientist and someone broadly sceptical about parapsychology, which really brings this irrational component home is this. After a lecture at the Royal Institution on PK metal-bending, one physicist sitting close to Dixon leapt to his feet and shouted, 'It's all nonsense. Nonsense! Heard it all before! Nonsense!' Dixon stated that he was so purple that he, Dixon, worried for a moment about whether the man might have a coronary or not. What is it that drives normally sane enough people to such extremes of virtually speechless irrationality?
We are familiar enough with irrational belief. There are some people who will believe almost anything. But, on the other hand, there are people who will refuse to believe anything. A perfect example would be the great scientist Helmholtz: 'Neither the testimony of all the Fellows of the Royal Society, nor even the evidence of my own senses, would lead me to believe in the transmission of thought from one person to another independent of the recognised channels of sense.' Here we have irrational disbelief: just another Lavoisier. Helmholtz has put himself beyond the pale of science: not the testimony of every single Fellow of the Royal Society would persuade him to revise his irrational disbelief. In short, Helmholtz has stated: My mind is made up and no evidence is going to change it. Now, whatever rules science has (and these, are constantly debated), this nonsense violates most of them.
So, why is irrational disbelief not seen for what it is? Why do newspapers detail excesses of gullibility but remain silent on this issue? Possibly because the irrational disbelievers have played a classic con-trick on us: they have pretended to be the 'real' scientists, defending the purity of science against the dangerous nonsense of parapsychology. But they may be seen, on closer inspection, to be nothing of the kind. Indeed they are not sceptics at all!
Consider what the irrational disbeliever is saying. First, there are certain Laws of nature (and the sceptic will frequently use the disreputable tactic of appealing to authority, in Inquisitional vein, here) - and psi contradicts them (which cannot be stated, as we've seen). Therefore psi cannot possibly occur, and one can dismiss any 'evidence' for it on any grounds which happen to be convenient - bad experiments, fraud, conspiracy, that kind of thing ('arguments' which contravene all rules of scientific discourse).
The parapsychologist is the true sceptic. He says, 'There is evidence, of the existence of Phenomena not generally accepted by science, and not incorporated into scientific theories. I am not prepared to accept it on the word of some authority (or group thereof) that these things cannot possibly exist. I question orthodoxy, and if you define dissent as heresy, so much the worse for science. I'm going to look at the facts without preconceptions.
New knowledge is often acquired by people who refused to accept the so-called Laws of nature, and authoritarian pronouncements about what was possible and impossible. Parapsychologists are in this tradition. They have generated new knowledge.