For too long the Horde have cornered the market on War Crimes, Genocide and general Evilness.
Make the Alliance the aggressor. Make the Alliance do somethin so disgusting, reprehensible, disturbing that Horde players can point to it and go "Yeah we’re bad, but the Alliance did (unspeakable thing here).
For all the new people or PVP junkies. Here’s a brief, incomplete history of the Horde.
Orcs on Draenor:
Drink Demon Blood. Commit Genocide against Draenei at Shatrath and what would become the Black Temple along with several villages. Later the Orcish Horde would use the skeletons of their victims to build the Path of Glory on Draenor (Outland) that lead to the Dark Portal.
Orcs on Azeroth:
Demon blood addicted Orcs invade Azeroth Eastern Kingdoms. They proceed to murder, pillage, plunder, rape and violate their way through Stormwinds outer villages and Stormwind itself. Basically Warcraft 1
Meanwhile:
Our friends the Trolls:
Eating, murdering, sacrificing Humans and High Elves (Later to become Blood Elves). They also do the same to each other, so there is that.
Flash Forward to the (and I use the word NEW in the loosest possible terms) New Horde:
The Horde under Thrall had slavery. Varian and Valeera Sanguinar were enslaved arena fighters.
During the Northrend Campaign to defeat Arthas (The Lich King):
At the Broken Front Gate. The Alliance assualted the undead forces and were ambushed by the Horde from behind. Instead of assisting the Alliance to secure the gate, the Horde killed the Alliance soldiers, giving Arthas more undead for his forces.
Battle of Angrathar, Putriss murdered both Horde and Alliance champions with the Plague while they assaulted the gate. Putriss was the Undeads chief apothecary and plague expert. Varimathras was blamed by Sylvanas as betraying her and the Horde and instigating the whole affair via Putriss. Later we would go on to learn that the Jailer and Sire Denathrius were responsible for the planning of it. The same Jailer that Sylvanas would go onto serve.
Warchief Garrosh Hellscream ordered the annihilation via Arcane Bombing of Theramore. A city governed by Jaina Proudmore, the same Jaina that pioneered peace with the Horde under Thrall.
The Horde would also invade Gilneas and murder the Heir to the Gilnean Throne amongst many others.
During the Mists of Pandaria: The Horde used Dalaran (a neutral city) as a hub to plan the infiltration of Darnassus to steal the Divine Bell. A misadventure that resulted in the rightful expulsion of Horde citizens and mages from Dalaran. It also ended with the attempted murder of Anduin Wrynn by Warchief Garrosh.
Finally, The Horde under Sylvanas burned a World Tree, Teldrassil. Resulting in the near exinction/genocide of the Night Elves and the extinction of several species found only on Teldrassil.
Now theres a whole books worth of other things, all of them involving murder or mass murder.
But, now you get the point.
The Horde has had the market on villainy for too long. Blizzard, give the Alliance a chance to show the Horde how it’s done!