Science depends on hypothesis generation, and reductionism says nothing about how to do that in a rational way, only how to test hypotheses rationally.

You may be interested in Science Doesn't Trust Your Rationality, in which Eliezer suggests that science is a way of identifying the good theories produced by a community of scientists who on their own have some capacity to produce theories, and that Bayesian rationality is a systematic way of producing good theories.

Oh, and Welcome to Less Wrong! You have identified an important point in your first few comments, and I hope that is predictor of good things to come.