I agree with what your doctor friend said. I don't agree with your last sentence since you have to have a provable vaccine for "herd immunity" to work. Do you mean "natural immunity" as in Measles ? Here is a quote from the article I posted"
"Herd immunity is community or group protection that happens
when a critical number of the population is immune to a certain disease. It can help stop or slow the spread of an infectious disease like measles or swine flu.
The safest way to get immunity is through vaccination. You can also get natural immunity by contracting the illness and building an immune response to it.
Herd immunity isn’t the answer to stopping the spread of SARS-CoV-2, the new coronavirus that causes COVID-19. Once a vaccine is developed for this virus, establishing herd immunity is one way to help protect people in the community who are vulnerable or have low functioning immune systems."