Moreover, it is not clearly to the skeptic's advantage to rely heavily on the Argument from Human Bias. For one thing, because human biases are not limited to the domain of the paranormal, the application of the argument extends beyond the boundaries of parapsychology. For example, we could use the argument to challenge every scientific lab study based on instrument readings and ordinary human observation. After all, scientists have at least as much at stake, and therefore at least as many reasons for perceptual biases, as do witnesses of psi phenomena. In fact, they may have more, given the intimate connection between their lab work and career interests. Furthermore (and even more important), the Argument from Human Bias cuts two ways, against reports by the credulous and the incredulous. If our biases may lead us to malobserve, misremember, or lie, then we should be as suspicious of testimony from nonbelievers as from believers. If (based on their favorable dispositions) we distrust reports by the apparently credulous or sympathetic that certain odd phenomena occurred, we should (by parity of reasoning) be equally wary of reports by the incredulous or unsympathetic that the alleged phenomena did not occur (or that cheating occurred instead). Although philosophers and scientists who fancy themselves to be tough-minded and impartial are often reluctant to concede this point, there have been exceptions. (The Limits Of Influence [Lanham, Maryland: University Press of America, Inc., 1997], 26-27)
He quotes C.J. Ducasse:
…allegations of detection of fraud, or of malobservation, or of misinterpretation of what was observed, or of hypnotically induced hallucinations, have to be scrutinized as closely and as critically as must the testimony for the reality of the phenomena. For there is likely to be just as much wishful thinking, prejudice, emotion, snap judgment, naiveté, and intellectual dishonesty on the side of orthodoxy, of skepticism, and of conservatism, as on the side of hunger for and of belief in the marvelous. The emotional motivation for irresponsible disbelief is, in fact, probably even stronger - especially in scientifically educated persons whose pride of knowledge is at stake - than is in other persons the motivation for irresponsible belief. (27)
Braude goes on:
Ducasse's caveat about irresponsible disbelief is buttressed by a wealth of evidence. For one thing, according to Stevenson (1968, p. 112), experiments have revealed some interesting ways in which peer pressure and other contextual factors can apparently influence a person's perceptions or perception reports. But even apart from the experimental evidence, the history of parapsychology chronicles an astounding degree of blindness, intellectual cowardice, and mendacity on the part of skeptics and ardent nonbelievers, some of them prominent scientists. (27)
Regarding the significance of bias in general, whether the bias of believers or unbelievers, see here.
