Empiricism in the philosophy of science emphasizes evidence, especially as discovered in experiments. It is a fundamental part of the scientific method that all hypotheses and theories must be tested against observations of the natural world rather than resting solely on a priori reasoning, intuition, or revelation.
This is why the ideologically compromised attempt to denigrate science. Like Toto in The Wizard of Oz, it looks behind the curtain of god-existence bluster, and social theory moralizing.