I often seem to come across people who express the sentiment in the title, and I've always found it pretty obnoxious. Aside from personal taste, when people try to explain why the Horde is better than the Alliance it often just seems to come down to "The Alliance/Humans are racist". Seriously?
The Humans arguably have fair reason for not trusting the Orcs given that they were responsible for two massive wars against the humans whilst possesed by demons (I'll admit im not a lore expert), and aside from that the Horde allows straight up evil people and factions to be members. The Bilgewater Goblins are led by a guy who sold his own people into slavery, the Forsaken and Sylvannas seem to betray or screw over both the Alliance and other members of the Horde regularly, the Blood Elves are all insane magic addicts, blowing up Theramore for no reason, so on and so forth. And lets not forget we just had an entire expansion where the Horde's new Warchief almost unleashed an ancient evil on the world and did all sorts of evil stuff, yet we're not meant to blame the Horde as a whole because it was apparently all entirely Garrosh's fault.
Maybe I've got some stuff wrong, if so tell me, but I can't really see why we get Horde players who act like the Horde are the poor downtrodden underdogs who keep getting oppressed by the mean Alliance.