Originally Posted by
Defengar
Aside from watching the orcs destroy his home city, kill his father, and then kill his mentor as a child, He was enslaved and used as a gladiator by the orcs at one point.
Oh, and before wrath when the horde and allaince got together for peace talks, guess who Thrall brought with him as an adviser? The Orc who fucking owned Varian and forced him to fight.
Even after seeing him there Varian still wanted to finish the talks, but Garrosh was there too, and his retardedness after a twilight hammer attack on the city ruined what had been accomplished. Also, Garona, the orc who had pretended to be on the side of humans during the first war, and had assassinated Varians father and cut out his heart was part of the attack, which brought up a lot of bad feelings in Varian.
What he said was because of that, and also because of what he had seen while in the UC.
From Wowpedia:
"When entering Undercity, Varian becomes disgusted by the condition of the once great city, which he had known since childhood. Tracking Putress to the Apothecarium, Varian and Jaina defeated him. But to Varian's horror, they also discovered dozens of mutilated and defiled human corpses, on which the Apothecary Society experimented on to create the New Plague. Realizing that, although the Alliance and Horde agreed to a small truce over the years, the Forsaken had been secretly creating a means to kill them all."