@TheSunIsStillShining
I don't know why you're adopting such a patronising tone. Are you an expert? On what? You seem extremely confused about the data. Of course the IFR of covid isn't 10%, even across the entire population!
The recent Nature paper I linked to argues that 50% is the threshold for herd immunity. If, say, 41% of the population acquired immunity through volunteering for inoculation, then we would be very close to the required number even if not one other person was infected (which won't happen). 7% of the population already has antibodies. (Of course, antibodies don't seem to last. There's a lot about long-term immunity we don't know. People might have to be infected multiple times, just as they might have to be vaccinated multiple times.)
However, once you take into account non-homogeneity, that 7% is effectively much higher. And some scientists have said that transmission is dramatically reduced with only 20% of people having antibodies. There may be some level of pre-existing immunity from exposure to other coronaviruses, etc.
But, just to disprove the idea that there would be millions of deaths... If we use one data-driven recent best estimate (fairly high compared to the CDC measures) of the IFR then we would expect, IF 100% the population was infected, the following:
Population data: www.statista.com/statistics/281174/uk-population-by-age/
IFR data: www.medrxiv.org/content/10.1101/2020.07.23.20160895v4
0-34: 28.8 million people
IFR: 0.01 = 2880 deaths
35-44: 8.4 million people
IFR: 0.06 = 5040 deaths
45-54: 9 million people
IFR: 0.2 = 18000 deaths
55-64: 8.2 million people
IFR: 0.7 = 57400 deaths
65-74: 6.7 million people
IFR: 2.2 = 147400 deaths
75-84: 4.05 million people
IFR: 7.3 = 295650 deaths
85+: 1.65 million people
IFR: 27.1 = 447150 deaths
Scary stuff! This gives a total number of deaths FAR higher than anyone has forecast because there's no disease on earth that is able to infect everyone! (In addition 7% of the population already has antibodies. And some of the most vulnerable people in the older age groups have, sadly, already succumbed.)
You can still see that the total number of POSSIBLE deaths in the entire population, including the very sickest and most elderly, comes in at under 1 million people. And that's using IFR rates that are on the higher side of recent estimates.
The point of asking only younger people to volunteer, and then screening them carefully, would be to achieve an effective level of herd immunity with a very small number of deaths. Most young adults who are vulnerable to covid can be identified in advance. Obviously we wouldn't be trying to inoculate people with a organ transplants, receiving treatment for cancer, with autoimmune diseases, diabetes, etc! Screening should also be able to identify some people who are more vulnerable than they might think, e.g. people with undiagnosed cardiac problems. The point is reducing the total number of deaths by creating a social 'shield' of those who have been infected and recovered. At that point, the pandemic will start to burn out and older and more vulnerable people will be able to live their lives again.
It would be better to achieve herd immunity via a vaccine, of course, but there isn't one. Chris Whitty says it will be at least another year before one is available. So the question is, how do we reduce total deaths between now and that point?
Strategic infection ought to lead to fewer total deaths than on-off lockdown for the next year. However, the deaths would be shifted into a different group of people. As in war, which has historically increased mortality in men from 18-45 or so, in a completely disproportionate way. Maybe in 2020 we would prefer to let a larger number of old or sick people die than a smaller number of young and healthy people? Personally, I don't like that idea. I would prefer to take my chances for the greater good. (Admittedly I have already recovered from covid and am not bothered about getting it again.)
Once you introduce the problem of collateral deaths a) because of the NHS being overwhelmed and/or suspending and delaying other medical treatments and b) because of poverty, hunger, reduced living standards and poor mental health, the numbers of deaths produced by even the most stringent and economically destructive lockdown are, imho, going to be unacceptably high over the next year. In the long run, it looks even worse...