I don't have to agree with someone else's political beliefs - or even generally like that person at all - to sell them a widget or buy from them a tool or raw-materials package; all I need are skills and a profit margin.
Indeed, and we are able to do so via the artifices of trade and commerce - the only thing that need be agreed-upon is the price, the quantity and the quality.
I can't say I like the grandparents "robotic" tone, but I have to disagree with you here on what all is required for coordinated efforts. People disagree locally on norms and etiquette all the time precisely because we are not robots. In fact the simple mechanism of agreeing on a price allows us to coordinate our activities despite disagreeing on so much else. Our differences play a role in making us human. So does our ability to coordinate without all being of the same mind.
On a larger scale, trade persists across legal divides - with much of this facilitated via contracts, which are actually not excluded by the grandparent comment. Here what I am really claiming that contracts are a form of generalized price. So trade, coordinated work, productive efforts large and small, are basically all facilitated by people coming to agreement on price, one way or another (unless the type of coordination involves a group of friends coordinating via friendship - or maybe some generalized version of that). The "price" agreement itself may be long winded (e.g. a contract with many conditions) but it is the basic mechanism of price that coordinates so much. Even world peace. Nations that trade together are less inclined to go to war with one another. (Absent a coercive situation that is. Without coercion, trade is mutually beneficial, by the standards of the parties willfully involved, and nobody wars with their benefactor)
Therefore, I would argue that we only need generalized prices (and a lack of coercion) in order to coordinate peaceably. We do not need to agree on norms and etiquette. Of course, if one party decides to spoil things and coerce another into a bad deal, or into conforming to its norms, etc., law becomes more important. (Of course in reality somebody always tries to spoil things so law is important from the very beginning, especially locally. I might argue that law becomes weaker anyway as we scale up towards nation state scale coordination where laws differ on both sides and contracts sort of blend into treaties). I am making broad statements about large scale action and I don't like that. Maybe better to sum up the position by saying given basic conditions - 1. property rights that try to be consistent, 2. dependable and consistent legal protection, and 3. a functioning price system (the less manipulated the better), we can coordinate imperfectly, but better than expected given the vast swaths of differences of opinion, taste, and preferences, that make us so human.
I'm talking about the hundreds of thousands of years we spent as tribes of hunter gatherers. We still carry much of the social needs and behaviors formed in that landscape.
Right, and I'm saying that the landscape has changed enough that many of the behaviors and characteristics we evolved back then, are maladaptive today; just because most humans happen to have a certain trait, does not mean that others should hold that trait sacred and kowtow+mold themselves to it.
There are other examples, too; ones with even fewer exceptions. Our minds and bodies both help hoard energy; that trait-set was useful when animals were difficult to hunt, but today it just foments carb-poisoning, obesity and a raft of other pointlessly energy-efficient design tradeoffs. (The modern world is so much more energy-abundant than the ancestral landscape, yet we can't actually make use of anything past ~8 MJ a day for anything but high-endurance physical exertion. A human brain is like a Pentium II hooked up to a 500W PSU.)
The fact that you engage in this discussion here seems a strong indicator to me that the landscape has not changed that much. Otherwise you would just exploit everybody around you, and not talk about it.
