I think we can say even now that herd immunity was the wrong choice, even not knowing the final outcome. The UK government's change of direction is a tacit admission of this fact. You are trying to defend the government's choice, or at least minimise their culpability, as they based their decision on advice from experts. Let's assume that there was more than one expert in the room and one was arguing herd and the other immediate lockdown. They chose wrong. Irrespective of any other argument, projected casualty numbers, ultimate outcome, whatever, they took a gamble that the infected would develop immunity but they didn't know if that was the case and still don't.
The lady on twitter is an academic. Northern Irish maybe as her bio says she studied in Queens and Cambridge. If you read the thread (not sure you did) then taking it as an anti-English rant (which it is not) is missing the fundamental points she is making, which is a shame.
I agree that there is a tradeoff to be made between the harsh economic impact, of which we have only had a taste of so far, and the number of lives lost but that is not a decision to be made at the sharp end of a pandemic when so little is know IMO. This thing is only ramping up really. In less developed countries then this decision would need to be made far sooner but the UK is still able to take a few body blows economically. The herd immunity is an approach which puts the economic outcome front and centre, whereas more left learning governments have out health outcomes for people first. That's the way it appears to me anyway. Also, it seems to me that all the best responses have been from countries led by women(just an observation)