Yea the horde bombed a school of neutral druids, nuked a city with a WMD the proceeded to capture the survivors and pit them against each other in fights to the death, used their corpses as target dummies, or used them as throphies hanging them from spikes. Even if the last part is largely done by garrosh's true horde. The horde still had a hand in the capture.
They then proceed to burn a tree with atleast 999 people left inside (occording the alliance only quest during the war of thorns) so its likely more seeing as in game numbers are almost always lower than actual numbers, but thats up for debate.
After that they attack a town that isn't part of the alliance yet and nail people to the wall,
My point: The Horde always goes out of there way to create as mutch collatoral damage as possible with or without Sylvanas.
The alliance atleast has the common decentcy to keep collatoral damage to a minimum, even if and when they do morally wrong stuff.
To give you an example the horde acts like 'the Major in Hellsing Ultimate' trying to create as mutch death and destruction as possible, and this is accross the board from high ranking officer to the common grunt.
You can count the alliance characters that show this behavior on one hand and have fingers to spare
Also @
sam86 that slaughter your talking about was during king Thoradin's reign wich was a 1000 years ago, before the alliance founded by king theranis menethil was even a thing, hell lordaeron wasn't even a thing yet.
So stop trying to scrape the barrel