Why Are We Killing Horde Heroes?

Why does it seem that in these raids we are always either killing unaffiliated characters or some sort of Horde hero? We havn't killed any Alliance heroes and it just seems like blatent favoritsm.

Karazhan: Prince Malchezzar - Unaffiliated
Zul-aman: Zul'jin - Horde Hero
Gruul's Lair: Gruul - Unaffiliated
Magtheridon's Lair: Magtheridon - Unaffiliated
Serpentshrine: Lady Vashj - Unaffiliated
Tempest Keep: Prince Kael'thas - Horde Hero
Black Temple: Illidan - Unaffiliated

Since the "Oh he went crazy with power and you have to kill him now" seems to be the favorite explainations of these encounters, why can't we see some of that for Alliance characters. If all of the sudden Blizzard released a new raid and said the final bosses were Alleria Windrunner and Turalyon because "they went crazy and decided to support Deathwing, you have to kill them now" people would go crazy and yet no one seems to have a problem with going and killing Kael'thas.

Am I the only one bothered by this?

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Edit from later post:


I think it would be better to say that we spend our time killing mainly characters that share the same race as the Horde races:

MC: N/A
Ony: N/A
ZG: Trolls
BWL: Orcs
AQ20: N/A
AQ40: N/A
Naxx: N/A (Human undead)
Kara: N/A (Human ghosts)
ZA: Trolls
Gruul: N/A
Mag: Orcs
SSC: N/A
TK: Blood Elves
Hyjal: N/A
BT: Orcs/Blood Elves

If you see, we're fighting either races that arn't on either side, or we're fighting the same races that are on the Horde. I don't count the human undead in Naxxramus and the Human ghosts in Karazhan because they are dead. We don't face living ones.