Herd immunity has fuck all to do with this in all honesty.
Look at chicken pox - ok we have 'herd immunity' to that. Everyone gets it eventually, but we don't have epidemics.
But the plan with this, is to let it run to an epidemic, so we don't get an epidemic in future? That's nonsense.
And the problem is clearly the number of cases at one time
We KNOW what percentage of CV19 patients need intensive care, and we KNOW damn well the NHS can't manage that if a lot of infections happen at once.
So compressing the epidemic into a lot of cases in a short space of time, is going to cause a hell of a lot more deaths than it needed to.