It’s our favorite vice and our true national pastime: Here in the land of plenty, Americans love to overindulge. We eat too much, drink too much, snack too much, sit too much — then rely on the marvels of modern medicine to repair our battered bodies. And that makes us easy prey for a brand-new infection like the novel coronavirus. “This is on us,” Nicole Saphier, MD, told The Post. “We left ourselves vulnerable to this epidemic. Our health-care system would not be so overwhelmed right now if it was not already overwhelmed with our preventable chronic illnesses.”