It means that they gather and interpret their material fairly and argue about its interpretations rationally.
( It ( ( means ( that ( they ( ( ( ( ( ( gather and ) interpret ) ( their material ) ) fairly ) and ) ( ( argue ( about ( its interpretations ) ) ) rationally ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ means) (SBAR (IN that) (S (NP (PRP they)) (VP (VP (VB gather) (CC and) (VB interpret) (NP (PRP$ their) (NN material)) (ADVP (RB fairly))) (CC and) (VP (VB argue) (PP (IN about) (NP (PRP$ its) (NNS interpretations))) (ADVP (RB rationally))))))) (. .)))
They gather and interpret the material fairly and argue rationally about it.
( They ( ( ( ( ( ( ( gather and ) interpret ) ( the material ) ) fairly ) and ) ( ( argue rationally ) ( about it ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VP (VB gather) (CC and) (VB interpret) (NP (DT the) (NN material)) (ADVP (RB fairly))) (CC and) (VP (VB argue) (ADVP (RB rationally)) (PP (IN about) (NP (PRP it))))) (. .)))