[Legate of Amon Lanc]

First, to your second question: surely. As there's already enough xenophobia even among humans as they are, imagine what would happen if an completely new species would appear. I can imagine gangs of "let's get rid of the pointy-eared freaks!" racists.

To your first question I answer with a question: do you think how men are treating Earth now is any different from how the men of, let's say, Beleriand were treating Earth? And it's not only about Earth in the ecologic way - the modern man can do much more to the nature than a man several hundred years ago, of course, which means that his actions have more impact even on the ecosystems. But if you say you think Eru would not be happy with how men are treating the Earth, then I'd say of course, but then I think he wouldn't be happy in the first place with how they are treating each other. And this is not just a matter of today, this was a matter of ancient times on our Earth and of Middle-Earth as well. And if nothing happened to Men there, then I don't see why would Eru do anything with today's men, if he suddenly appeared in our world. But this is a little bit off-topic, since I thought we were speaking about Elves, not Eru. After all, these Men are not even his Children. Or rather, Eru is not in our universe. You could imagine Elves appearing here quite easily, but Eru is something that has impact on the entire cosmology.

Back to the Elves - and what do you call "modern man"? I mean, if you had the Three Kings of Eldar suddenly mustering their hosts on the plains of Kazakhstan, who would they march against? Or what will they do? Or will several Wise find shelters, build New Lórien in the forests of Amazonia and New Rivendell somewhere in Himalayas and New Havens on some remote island in the Pacific, and there make councils trying to find ideas how to... how to what? Here is no single, specific enemy, no "Sauron" whom they could march against. Or what is that you have in mind?