Look, if anyone in America is at fault for lack of immunity to disease and lack of technology, it's the North! No light bulb went on inheir heads when they interacted with the Vikings in Greenland, for example? Apparently, not the right light bulb.
And that's not to mention the island chain on the other side stretching from Alaska. No. Nothing. Tens of thousands of years go by and the North Americans? Dancing around with few clothes on worshipping albino buffalo. Absurd! Not right in the head. If a fool's errand to speak to them, understand: the messenger (imperfection assumed) may only be a fool due to audience error. You can't save some people, unfortunately, but, if you warn them to repent, perhaps, their blood is not on your head?