I’ve worked very hard in this book to keep the lines of communication open. I don’t want to turn someone away from this information for partisan political reasons.

Diamond is emphasizing a deliberate rhetorical strategy: to present contentious, policy-relevant material in a way that remains accessible across ideological lines. The “lines of communication” metaphor suggests that facts and arguments can be blocked not only by ignorance but by identity and party loyalty; his aim is to reduce that blockage through tone, framing, and careful sourcing. Implicitly, he treats the subject matter as urgent enough that persuasion and shared understanding matter more than scoring partisan points. The quote also signals an authorial ethic: scholarship should be communicated so that readers who might disagree politically are not pre-emptively alienated from the evidence.