Second, because scientists are human beings, and because human beings tend to resist the overthrow of their most cherished beliefs, scientific theories, once accepted, are often exceedingly difficult to supersede. The shameful treatment of Pierre Duhem at the hands of his institutional superiors is a well known case in point. All too often, the new, even when it carries great weight of evidence, gets routinely derided as outlandish. That scientists are intellectually conservative, of course, is good. Their conservatism helps protect them from the multiple embarrassments of intellectual trendiness. But that scientists are unduly entrenched, when they are, is lamentable. That entrenchment reveals that scientists sometimes are, like the rest of us, resolutely unteachable. Scientists who think in that fashion seem to me to be what one dictionary defined as "proof-proof:" the state of mind of one upon whom contrary evidence and argument have no persuasive effect, regardless of their strength. I am not alone in this observation, of course. Many writers, Kuhn and Laudan among them, have shown how dogmatism -- yes, dogmatism -- characterizes the periods of what we might call normal science. Whether we want to admit it or not, there is a remarkably comprehensive scientific orthodoxy to which scientists must subscribe if they want to get a job, get a promotion, get a research grant, get tenured, or get published. If they resist, they get forgotten.
Given how changeable previous scientific world views have been, one wonders how chimerical they would have proven without this dogmatism. I am not here debating the relative merits or weaknesses of dogmatism; I simply say that scientists are by no means free from it and should not be treated as if they were, or permitted to speak and act as if dogmatism were a characteristic only, or even primarily, of theologians.