That is... not a good description of herd immunity at all. It has nothing to do with vaccinations or time scales. Wikipedia's is quite clear: https://en.wikipedia.org/wiki/Herd_immunity
The idea is that once a significant fraction of the population has some immunity to an infection, the ability of an infected person to spread the virus (a term called "R0" in the jargon) is fundamentally impeded by its ability to find infectable targets. So the R0 drops, and so does the exponent to the growth. Once that exponent goes below 1, the number of cases drops over time instead of growing, and new infection clusters can't start.
This works. It's why we don't have things like measles outbreaks (or didn't, until the anti-vax crowd messed things up) and why newly mutated flu strains can't find purchase and become pandemics.
You seems to think that people who is against the idea either doesn't understand what herd immunity is, or doesn't understand the plan. We understand both, we just think that the risk analysis is wrong.
Specifically with the GP, his argument is that herd immunity gaining through large percentage of the population being infected in a short amount of time is a bad idea. Normally we got herd immunity via vaccination of the population, since it is much safer than being infected. That's why vaccination was mentioned.
The idea is that once a significant fraction of the population has some immunity to an infection, the ability of an infected person to spread the virus (a term called "R0" in the jargon) is fundamentally impeded by its ability to find infectable targets. So the R0 drops, and so does the exponent to the growth. Once that exponent goes below 1, the number of cases drops over time instead of growing, and new infection clusters can't start.
This works. It's why we don't have things like measles outbreaks (or didn't, until the anti-vax crowd messed things up) and why newly mutated flu strains can't find purchase and become pandemics.