That's a scary mentality to have. For one, we still don't know...

That's a scary mentality to have. For one, we still don't know how long antibodies last, and if they stop reinfection.

And two - assume that figure is right, 20% of New York has antibodies. You need around 80% for herd immunity. So 4 times the cases in New York, and 4 times the deaths. 28,868 deaths currently, would say you'll get 100,000 people dead in New York before you get herd immunity.

Extrapolate that - about 6000 deaths per million (New York figurea). US total population of 328 million, this would be about 2 million deaths in the US. 0.5% of the United States dead. While Orange Man says he won't close down again, being the POTUS who allows 0.5% of population to die wouldn't go great for him.