We partake of [victims of injustice’s] uneasiness by sympathy; and as every thing, which gives uneasiness in human actions, upon the general survey, is called Vice, and whatever produces satisfaction, in the same manner, is denominated Virtue.... [S]ympathy with public interest is the source of the moral approbation, which attends that virtue" (II.ii)
I think the zone of benevolence might not create the kindness, but merely allow it. Many people would be kinder if it wasn’t a sign of weakness or weirdness. If there’s an area where kindness is permissible, where you can still look cool, and it’s unlikely you’ll be accused of an ulterior motive, then perhaps people would jump to help one another. Helping someone often translates to, “You owe me” which is an uncomfortable place to be. To build a benevolence zone, then, would require a foundational belief that we can give without expectation of receiving.