That's just it, the Alliance AREN'T good. They're racist (they kicked out the Blood Elves for changing their names), they've created all the major villains in some way (Illidan, Medivh's creation of the Horde, Arthas AKA Daddykiller, AKA the LICH KING, Nathaniel Blightcaller, Major Samuelson being a Twilight Cult infiltrator, and you could probably lay most of the Troll trouble at the High Elven feet. Not to mention the Naga and Satyr being of Night Elven descent) there are very few actual Horde 'villains' other then Gul'dan, and HE was tempted by Medivh. Hell, even the Draenae (Sp) were part of the Burning Legion as the Eredar.
If you want the TRUE Heroes of Azeroth, play the Horde. They're the goodie too shoes of Warcraft. You want to play a villain, go Alliance. That's where the evil is at.
That's not true with the Blood Elves by the way..and the Dranei that came to Azeroth were the ones that DIDN'T convert to the Burning Legion.
Blood Elves are magic addicts. Always were. With the destruction of the Well of Eternity, they split off from the Night Elves and set up the Sunwell. They were the High Elves then till Arthras destroyed it. Then their leader turned to feeding on Fel Blood and Magic to stave off their addictions, that was when they became Blood Elves (Named so by the Prince to memorialize the fallen of Silvermoon).
Blood elf paladins stole power from a Naruu to fuel their powers.
With the re-ignition of the Sunwell, there is a chance for them to step back from the brink. But they aren't innocent victims but addicts who did what they had to satisfy their needs. Remember they allied with Illiadan and the Naga, only when Kael'thas' duplicity came out did any large faction of them break with him. (The Scryers)
The Draenei crashed do to the interference of the Blood Elf/Burning legion. They were the Eredar that DIDN'T turn to the legion and allied with the Naruu.
Basically, in my opinion, both sides have good and evil in them. Some of it from scars from war (Humans/Gnomes), some of it schism within themselves (the Dwarves), others it's their drives (Goblins) and for some it's their nature. (Undead). I don't think the Orcs, Trolls or Tauren are outright evil, but they have made some BAD calls to maintain their equilibrium.
Taking in the Undead..definitely. The Blood Elves possibly. The Goblins? Not sure. Appointing Garrosh Hellscream as warcheif was a mistake. He's more likely to split the Horde than the Alliance is.
The Alliance is several bombs waiting for the right fuse though. The humans have schisms that are waiting for the right hammer to split them and the Dwarves are one council meeting from Civil War.
And I think the Horde with a savvy leader to have turned the Undead from Gilneas and avoided adding a new member to the Alliance.
(Yes, I read way too much lore of the game I play.
I find it sad the best bridge builders in the game, Thrall and Jaina Proudmoore, are in positions that prevent them from doing so. I think any hope of peace is moot till they make a move.