Here's what I have trouble reconciling: You say that this attenuated virus would spread automatically -- just like a virus -- and yet no one would be infected on purpose, only if people "chose to become infected on their own by hanging out with those infected with an attenuated strain".
How much agency do I have in whether I get infected or not? It seems strange to me if it depends on the genetic makeup of the virus.
If you were to deliberately go and hangout with someone you know is infected with the attenuated strain then a lot, if you catch it because your neighbour did this then none.
This discussion is really a distraction as I don’t think a “grass roots” spread would be the way any such strain would be spread. I think the regulatory agencies would look at the data collected from the natural spread and use this to approve the strain for use.
How much agency do I have in whether I get infected or not? It seems strange to me if it depends on the genetic makeup of the virus.