"Also, I might note that the Tauren welcomed the Orcs to Kalimdor, and didn't consider them "a pain in the butt", but saw their need, and helped them."

Did you actually read all the replies you've already got? Orcs intruded on the night elves' homeland, not the Tauren's. Tauren, as close to nature as they may be, are not particularly close to forests specifically; grasslands are more their thing. Night elves, on the other hand, live in trees and literally befriend some of them.

"Grom Hellscream and his orcs killed Cenarius. This was rogue action done without the Warchief's approval. Also, he was under the influence of Mannnoroth, a DEMON. If the Night Elves can't see that it was not the actions of the Horde, but of a rogue Orc that did it, well, I don't know what to say."

Grom wasn't *the* Warchief, but he was close to him politically and personally. And he chose to drink Mannoroth's blood - twice. You're expecting the night elves to have an unrealistic, nearly impossible level of willingness to extend good faith. Why? It makes no sense.