Say Mike Pence funded is own personal army and march on Mexico in a genocidal invasion. Even of the American government had no knowledge or involvement it would still look bad on them.
Arthas wasn't just a human, he was the heir to the strongest human nation on the planet. The Blood Elf survivors likely don't overly cafe for the nuisance of Arthas position and how that relates to the rest of humanity.
Blood Elves holding a grudge against humanity for arthas is understandable.
I agree them not holding a gruge for undead (Human undead at the very rate) and Orcs is a bit of leap of logic on Blizzards part.