Easily. I'm sure there are at least that many Americans who hate America.

But that's besides the point. I don't think unusual and extreme examples are very probative in determining how people feel more generally. I think that when you get as absurd a hypothetical as "erase the US entirely," the evidence provided by it is irrelevant.

That said, I do agree with you that, in general, people do not generally care about the overall happiness and flourishing of mankind. I think reducing the problems posed by jealousy would actually lead to significant individual gains for those involved, but it's such a gut reaction that I don't think people acknowledge this. Plus, less jealousy would probably mean less concern over commitment, which I expect would lead to more sex in general (among other things), and plenty of people have a problem with that.