Anecdotal evidence really doesn't mean much, but from any time I've seen any legitimate amount of WoW fans gathered, the Horde fans always seem to be more aggressive, self-aggrandizing, and believe they're the "cooler" of the two factions. I'm not sure why. Its just childish.
Its also the same reason why if Blizzard actually only making one of the bikes in the Azerothian Choppers thing, the Horde would obviously win. They care far too much about fighting to think they've "won" something that doesn't matter to the game whatsoever. Nobody cares if you scream louder than the Alliance fans at Blizzcon. If you like a certain faction lorewise, that's totally fine, but otherwise stop looking like giant tools.
You give the Warcraft community an even worse name by acting like a child.
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You fail to understand that its a snowball effect.