Reasons to leave the Horde:
1: Orcs smell and are fueled by testosterone.
2: The undead are cold-hearted and consumed by vengence, and are kinda also smelly and gross.
3: The trolls are smelly and eat people.
4: The tauren are okay, but all that cow under all that fur? Smelly.
Reasons to join the Alliance:
1: Highborne are smexy smexy. The tall, physically superior bodies and senses of night elves with the magical prowess of blood elves.(Probably better at it, but meh.)
2: Magical flying city of arcane death. Maybe we'll crash it into Orgrimmar and kill Garrosh, then the other Horde races won't be scared of getting killed in their sleep if they join the Alliance.
3: Smexy smexy humans.
4: Smexy smexy night elves.
6: Smexy smexy draenei.
7: If Varian fails, you know Malfurion's gonna step up and kick some !@#.
Please consider your options, Lor'themar! Jaina may be having that time of the month, but it's no reason to sacrifice personal hygiene! Plus I have fancy cheeses and wines.
P.S. If you think the game might be unbalanced, just give the Horde troggs or gnolls or a tribe of smaller Mogu.