I feel like there’s a bit of cross-talk going on whenever these kinds of awful events are compared, and this hyper-factionalized narrative just makes it worse.
A lot of arguments like this seem to eventually fall into the same rut:
“Look at this terrible thing the Alliance did!”
What they probably mean: “The Alliance does bad things, too. It’s not just the Horde, and the Alliance isn’t perfectly squeaky clean. It’s not a black and white fight.”
What the other side often hears: “Look at this! The Alliance is clearly just as morally bad as the Horde!”
(and in some bad cases: “Maybe even worse! I’m sure the Alliance dead deserved it somehow!”)
So, what they counter with: “Well, the Horde has done worse than that!”
What they probably mean: “Okay, yes, the Alliance does bad things. But one side kicks a puppy while the other murders people - the factions are far from equal right now!” (possibly with “ideally, they should be more equal, but they clearly aren’t.”)
What the other side often hears: “Anything the Alliance does is automatically excused by this thing the Horde did! Stop whining about your piddly losses, and how dare you besmirch the glorious perfect Alliance!” (spontaneously turns into male human paladin with a Garithos moustache)
And then this cycle repeats until everyone is too angry to keep talking to each other because they feel the other side is dismissing or ignoring their real argument.
Or, worse, one or both sides gets pushed far enough that they turn into that extreme perception of their argument.