That sounds like a bad moralistic fable. Neighbors advanced enough to instantly blast expanding civilizations that don't expand? If they don't expand why the hell would they care about others outside their domain? When compatible planets are so rare that essentially being able to survive in space indefinetly is essentially a logistical prerequisite to expand in the first place. They might compete over such viable luxuries if they find others in range good canidates but a radical antiexpansion ideology and said capabilities is deeply inconsistent.