He's a complete tosser.
This article, written by a Yale epidemiologist, really clearly explains it:
The basic mechanics of this mathematical principle dictate that even if there is only a little bit of additional connection between groups (i.e. social dinners, playdates, unnecessary trips to the store, etc.), the epidemic likely won’t be much different than if there was no measure in place. The same underlying fundamentals of disease transmission apply, and the result is that the community is left with all of the social and economic disruption but very little public health benefit.
Seemingly small social chains get large and complex with alarming speed. If your son visits his girlfriend, and you later sneak over for coffee with a neighbor, your neighbor is now connected to the infected office worker that your son’s girlfriend’s mother shook hands with. This sounds silly, it’s not. This is not a joke or hypothetical. We as epidemiologists see it borne out in the data time and time again. Conversely, any break in that chain breaks disease transmission along that chain.
It is hard (even for me) to conceptualize how on a population level ‘one quick little get together’ can undermine the entire framework of a public health intervention, but it can. I promise you it can. I promise. I promise. I promise. You can’t cheat it. People are already itching to cheat on the social distancing precautions just a “little”- a short playdate, a quick haircut, or picking up a needless item from the store. From a transmission dynamics standpoint, this very quickly recreates a highly connected social network that undermines much of the good work our communities have done thus far.
People need to grow up. Cheating the lockdown has hugely significant impacts, and unless anyone wants to kill people in the sort of numbers Ian Brady could only dream of, then everyone - all of us - must hold the line.