> you can't reasonably desire herd immunity if you can avoid it.
And that is the crux of it. Can you avoid it? If you can avoid it, by all means do it. If you can't you might as well make sure you reach herd immunity by infecting the least susceptible age groups.
The ability of the population to stay indoors is limited, _especially_ if they don't see the effects of the disease (because they are indoors, right?) so you can't be able to keep up the pace for 2 years.
This is basically a bet on whether the resolution will be reached through herd immunity or some other means, some drug or quick vaccine.
If you do get the resolution by herd immunity anyway, you want to infect the least susceptible population and sustain the highest economic activity and standard of life for the population. If this bet pays off, you're least affected. If it doesn't and some magic solution shows up, you will have already bore the brunt of your approach and more people will have died than they should have.
If you get some sort of technical, quicker solution to the problem, the you will have the least overall number of deaths and will have paid a comparatively small cost by doing a lock down for a couple of months only. If this doesn't pan out and you get my herd immunity anyway, your overall number of victims will be higher than the herd immunity folks because statistically the spread will be uniform through age groups and your economy will be in worse shape because more people had to stay at home for a longer time.
It's all in what you think is the most likely resolution to the crisis and how well you follow through with your plan. I am though of the opinion that if you're to commit to a strategy, commit to it fully.