I think the book specifically and explicitly covered the "dark forest doesn't apply when species are near one another" angle.

How far is "near," really? Human civilization took tens of thousands of years just to discover a new continent, and the ocean back then was essentially as vast and impenetrable as space is today. If we ever actually develop near-lightspeed spacecraft, are we seriously assuming the first thing we'd do is build weapons capable of annihilating entire civilizations — and then actually use them? Oh my god, we already have those weapons, and the most likely target has always been ourselves.