Isn't it probable that people most at risk are also more likely to spread the virus? They would shed much more virus, wouldn't they? So it's not so simple, someone who has a better functioning immune system represents a lesser risk to others. Is there a counterargument? I do recall some studies acknowledge this, but I don't have a reference.

Yes - the counter argument is that people who are asymptomatic or mildly symptomatic (think seasonal allergies or “it’s just a cold”) will go about their lives as normal. And this, for many, involves not washing hands after using the restroom, mild coughing and sneezing into their hand and touching things, and spreading germs through close conversations.

There were always people at the office that showed up with a fever, clearly exposing everyone on the bus and at the office, but for a large number of people, this is just one that we would have pushed through.

If you get covid with moderate symptoms, you (hopefully) stay home. People with severe symptoms go to the hospital or die. You don’t need to worry about those people being super spreaders. It’s the people that push through or feel mild symptoms and carry on without thought that are giving it to others, and those in turn may accidentally give it to the most vulnerable in their bubble.

And I hope when you or I get it, that it does feel just like a cold - or is even asymptomatic. But I know that for some percentage of the world it is not, and it will kill them.

This is probably too simple, but: Transmission = infectiousness x interactions. In your example, People with weak immune systems, who are more infectious, are less likely to have interactions.