Horde and Alliance alts throughout my time playing World of Warcraft, of course. With the exception of the Forsaken, I've always viewed the Horde as more or less morally equivalent with the Alliance. Sure, there were some things that bugged me, like naming the capital city of the Horde after Orgrim Doomhammer, a guy who enslaved the dragonqueen Alexstrasza and who went along with Gul'dan even though the warlock in question murdered his best friend and best friend's wife. But these were minor hiccups, and I especially loved the tauren, having leveled both a DK and warrior tauren to level 80 in the Wrath years.
Ironically, although I was somewhat negatively inclined towards Garrosh Hellscream, it wasn't until I switched factions on my main to play Horde with a new guild (and an excellent one, to be sure) that I started really, really hating the Horde. Every quest I've gotten so far on my main or my two leveling alts Hordeside has involved murdering people and stealing their land simply because I could (or because a guy using an axe I outgrew 15 levels ago says I should).
But it's done more than make me dislike the faction I'm playing. Paradoxically, it's made me fight really, really hard for that faction. I PVP a lot more now than I ever did when I was playing a worgen personally offended by what happened to Gilneas. For some reason, being in the Horde makes the semi-military feel of battleground PVP seem more like it has a point to me, as if I'd expect to find myself there. I'm more aggressive as a Horde player. My paladin has run through Desolace and now Feralas with abandon, thinking nothing of doing quests that massacre entire Alliance settlements for the crime of trying to continue to exist. For all that I often decry the Horde and its current Warchief, I'm certainly also part of the problem, because I'm the one doing the quests. I am the unprovoked fist of the Horde, crushing innocents and stealing their homes. Granted, I'm not known for my stability, but I have to wonder if anyone else has experienced this.