Ok I'm going to put this at the top since I believe it sheds further light on many of the points. This is a talk at UCSF's medical grand rounds (the weekly science talks given to all doctors at UCSF). At 38 minutes, one of the scientists cited by the MIT tech explains his findings in support of herd immunity. It's not peer reviewed yet because it's brand new- peer review takes a minimum of three months. He shows open table and google maps data in support of people not being much more careful in Florida or AZ. He also explains the interplay between mask wearing etc and RT. Hopefully you will find this to add extra rigor to what I have been saying. It is pretty dry- but that is the nature of this sort of talk. https://www.youtube.com/watch?v=Ew2MEF4XX8w.