It is one thing that the statistical results depend on the initial opinion of the scientist. But it may so happen that the scientist has no opinion whatsoever about the hypotheses. How is she supposed to assign a prior probability to the hypotheses then? The prior will have to express her ignorance concerning the hypotheses. The leading idea in expressing such ignorance is usually the principle of indifference: ignorance means that we are indifferent between any pair of hypotheses.  For a finite number of hypotheses, indifference means that every hypothesis gets equal probability. For a continuum of hypotheses, indifference means that the probability density function must be uniform. 