this is from the view of a system with only those two people. From the view of society then it is absolutely true that one person coming to harm would be something society would want to stop, and such an action would be immoral. However, from the view within only that system, there are only two actors, and they do not agree with one another, so no choice will be made, and as such, the system will be treated as if it can make no choices

If we considered an action that affected millions of people (a government leader) then this system would almost certainly fail to produce any actions in which everyone in the system (e.g. a country's population) wants a given action to occur. Therefore this system would not produce any moral actions and is functionally useless to that aim, which is something you agree with when you say:

I assume it cannot.

Which leads me to think that you're essentially saying: Any action that everyone wants to happen is moral. This isn't particularly groundbreaking. The real difficulty (and field of interest) is how to deal with actions where each outcome has pros and cons.

but the massive numbers of wars, fighting, psychopaths, and so on, clearly show that not all humans are concerned with total human wellbeing.

Now you're charting into some interesting ethical philosophy that compares which form of well being we should aim towards: total or average well being. To sum it up both sides have issues (called the Repugnant Conclusion, check my post history for the link + discussion):

"Total Utilitarianism" would essentially favor the addition of any life that is even marginally worth living. So having 500 billion humans with barely enough resources to survive (let's say 1 happiness point each) is favorable to a smaller population of 1 billion with much higher average happiness (let's say 100 happiness each). 500 billion 1 is greater than 1 billion 100 so the former is better than the latter according to Total Utilitarianism. This clearly is counterintuitive and not worth our time.

"Average Utilitarianism" states that having the higher average utility is favorable (take the above example and just flip which one is favorable). The issue with this is that this justifies enslaving a small population for the increase in average happiness for the masses.

My personal solution to the Repugnant Conclusion is to do what I mentioned earlier: add some rules to actions that have to be held for them to be considered moral. For me that rule is the preservation of justice (no infringing human rights like liberty, etc). This prohibits the idea that we should kill/enslave a minority to bring up the average happiness.

Thoughts?

For the points, keep the above on mind when rereading them.