This was origionaly a reply to a different thread but I realized I had written so much it had gone off topic. While I realize this topic is going to spark some angry responses I encourage everyone to read the details of what is summarized here, and read the articles for more information.
The good and evil argument of the horde can be broken down by looking at it as different entities at each point.
Horde's 1-3: Each of these group were literal armies bent on conquering and destroying, often being manipulated by outside forces. There is little to no argument that these orcs, orges, and more were all evil. For evidence we really need to only look at Alextraza and her suffering at the hands of the Dragonmaw.
Horde 4: Lets examine the order of events, and specifically the people associated with them.
Thrall, the beginning of a great hero. Thrall raised his people up from the ashes, freed them from what was a total dickmove by the Alliance, and still had the open mind to understand that his people could not simply take the lands they needed. Not one person who read those stories, Horde or Alliance, sat around feeling all giddy about what happened to Taretha, fucking Blackmoore got exactly what he deserved. Guided by a vision from Mediv Thrall took his people across the seas to a new land, meeting Vol'jin along the way.
Vol'jin, the shadow hunter. Vol'jin didn't ask to lead his people, it was forced upon him when his Father died. Thanks to the timely aid from Thrall and his Orcs Vol'jin was able to save his tribe of Darkspear trolls from certain death at the hands of murlocs and their sea witch, in turn he pledged his friendship and loyalty to Thrall. They continued their way to Kalimor where on its shores they would meet with Cairne Bloodhoof.
Cairne Bloodhoof, the most honorable cow. Where to start on this noble beef...there may never be another race leader with as kind a soul or as big of a heart as Cairne. When Thrall landed he discovered a native Tauren in need of assistance, being attacked by brutal centaurs. Without hesitation he jumped in to aid made a great ally who would later become a founding member of the Horde.
Now here is where things start to break down. The three leaders above, in their current forms, are kind, honorable, and have clear goals for peace and happiness for their people. But not all Orcs feel the same drive to nature and Shamanism that Thrall does.
Grom Hellscream, the angry puppet. Grom takes his first chance to start a war with humans, here is an excerpt from wowwiki on the events shorlty after Thrall and Cairne part ways.
"When Thrall arrived at the base of Stonetalon Peak, he was shocked to find Grom Hellscream and the Warsong clan battling humans under the command of Jaina Proudmoore. Her forces had cordoned off much of the pass up the mountain. Thrall considered hiring goblins to ferry them up the mountain in zeppelins, as it would allow them to bypass any defenses. However, as Thrall tried to make his way stealthily up to the goblins, the impatient Hellscream unexpectedly attacked the humans. Thrall confronted Grom, but Hellscream argued that "a true warrior" would have fought the humans without question instead of trying to sneak past them and avoid battle."
Sound familiar? Shortly after this Thrall meets Jaina and they form a pact to work together, because that is what was in the best interest of all parties. However Grom has already gone full circle and is now back under the corrupted influance of Mannoroth. Grom Hellscream was portrayed as a hero in death, having fought to overcome the control and slay Mannoroth, but his actions when not being controlled were warlike, close minded, and overly aggressive. While Grom was not evil he was indeed a total ass, and as long as he wasn't given leadership that works just fine in Thralls new Horde. Obviously more on this topic later.
Rexxar, the massive man of beasts. I wasn't going to touch on this one, but with the addition of Chen Stormstout to WoW it is much harder to ignore than it has been in the past. To keep this short I can say that both Chen and Rexxar prove themselves to be honorable good people, both in eyes of the Horde leaders and in their people. These two helped uncover what came to be a dark stain on the Alliance history of Kalimdor, the murderer Admiral Proudmore. While circumstance and motive can be argued for what Admiral Proudmoore was doing in the end he was pursing a war that ended long ago. But even in his death Thrall proved to hold his honor as a warrior above all else.
Lets pause here for a second. This is end end of Horde 4, a collections of Orcs, Trolls, and Tauren, with the occasional aid of Ogres and Goblins. I have rarely heard a player, on either faction, claim this horde to be evil, or attempt to defend the actions of those who stood in their way.
For more details on the path of Thrall read his wiki entry here: http://www.wowwiki.com/Thrall
Horde 5: The Forsaken.
This decision was made, I can only assume, because the designers of WoW knew that players would want to continue the story of the Forsaken. Given what we know about Thrall's Horde, and what we know about Sylvanas, it is very difficult to understand why Thrall would accept them into his Horde, thought not hard to see why she wanted to be.
Sylvanas Windrunner, the banshee queen. In the early days of wow, and end of WC3, we have a fair amount of character developed for the Banshee Queen. She is ruthless, single minded, and willing to use whatever weapons or tools she has available to achieve her goals. During parts of the Forsaken quest lines you are sent off to murder people, humans, simply because they are there, it is no secret that she desires to wipe out human(oid) life across the planet should she get the chance. A example of this would be shown much later during Gilneas when she almost eagerly brings in the Plauge to wipe out the natives.
Many specifics could be gone into with the Lady but safe to say, if you agree with her or not, she does not fit the mentality of the other Horde leaders at this time.
For more information of Sylvanas Windrunner read her wiki page here: http://www.wowwiki.com/Lady_Sylvanas_Windrunner
Horde number 5 continues for some time, through the events of Burning Crusade. And while there are certainly reasons on both sides of the fence that the Horde or the Alliance is confrontational the overall feel is still that of two different cultures looking to establish peace for their peoples future.
Horde 6: Return of Hellscream
Garrosh Hellscream, the self fulfilled prophecy. The flaws and crimes of Garrosh are well documented, his anger and frustration a constant thorn in the side of Thrall and his Horde. During the events of WotLK he did not do anything to help aid the war, in fact he distracted from it by having his commanders constantly start conflict with Alliance forces in Northrend. Despite all of this Thrall chose to show his largest lapse in judgment in history by putting him in charge at the beginning of the events in Cata despite there being countless better options (Cairne, Vol'jin, Saurfang to name a few).
Garrosh wants war, and he wants the power to end it. In truth he has become exactly what his father always was, a power hungry war monger who sees only battle in front him and nothing else. Fortunately for the Horde his goals only really align themselves with one other race leader, and even then only slightly, Sylvanas Windrunner. She is also aiming for the destruction and war, however has played silent to watching Garrosh destroy himself one day at a time.
For more information read this: http://www.wowwiki.com/Garrosh_Hellscream
Here is the moral if this essay: if you think that what Garrosh is doing with the Horde is fine and ok, you then do not believe in the Horde built by Thrall at the end of WC3. While some level of conflict is inevitable between the factions this unwarranted bloodshed, murder, and war mongering is not what these once proud races came together for. If you follow the ideals of Garrosh then you also probably follow the ideals of Sylvanas, who has committed more awful heinous acts of violence and death than any other race leader to date, though Garrosh is striving for the title.
Is the Horde evil? No. Is its leadership evil? Yes in the sense that they will choose war over peace when it comes to dealing with the other factions.
The best hope? Blaine Bloodhoof. He has the balance and understanding to lead the Horde, though some may say he lacks the experience to do so I disagree. Thrall was not experienced when he chose to lead his people to a new land where they could be at peace.
Note: This is written from an Alliance Player, one who had the great respect for Thrall before he donned his invincible bullshit plot armor of +10 Metzan. Also a druid since Vanilla who has the deepest respect for the life and culture of the Tauren people.
PS: Sorry for not covering Blood-elf and Goblin, they weren't as relevant to the conversation. But trust me they don't do anything to help the case of the Horde being less evil, a race of money grubbing thieves and a sect of elves loaded up on fel drugs doesn't exactly build a court case for a stable home environment.