And besides, orcs aren't the only ones who get manipulated into doing bad stuff by a bad guy.
Night Elves - Azshara and the Highborne were manipulated by the Burning Legion, and Fandral was manipulated by Xavius and the Old Gods. I suppose all Night Elves are naturally evil, then.
Dwarves - The Dark Irons summoned Ragnaros and served him to kill the Bronzebeards and Wildhammers. I suppose all Dwarves are naturally evil, then.
Draenei - Archimonde and Kil'jaeden, along with their two tribes of Eredar were manipulated by Sargeras. I suppose all Draenei are naturally evil, then.
Gnomes - That one gnome that infected Gnomeregan with leper gnomes was bad, so I suppose all Gnomes are naturally evil, then.
Worgen - Worgen actually have a hard time keeping their cool when provoked, and often lash out just like the Orcs. I suppose all worgen are naturally bloodthirsty and evil, then.
Humans - Arthas, Kel'thuzad, King Perenolde, Baron Rivendare, Renault Mograine, and many more were seduced by the promise of power or manipulated by Scourge, Deathwing, or the Legion, so I suppose all humans are naturally evil, then.
Orcs lead a harder lifestyle than humans, and have for generations. Therefore, they have a natural biological reaction when under pressure or in extreme situations where, if they're not careful, the bloodlust can take over. Drinking demon blood made this bloodlust much stronger, so they were in a constant state of it. When Grom killed Mannoroth, it lifted, and they could be free. Now if an orc loses their head, it's their natural reaction because they're not controlling themselves well enough.
In Draenor's case, the Iron Horde was not a result of bloodlust. It was a result of Garrosh telling them that if they didn't invade and conquer Azeroth, they'd all be enslaved by us. And they believed him because they thought he was a prophet who knew the future, because he knew certain details from history such as Gul'dan's attempts to seduce the orcs to work for the Legion.
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Exactly. She's a hypocritical egomaniac, and because Blizzard wanted her to be the victim and Garrosh to be the bad guy, they gave everyone amnesia so nobody mentions that Theramore was not neutral, and never address any of her bs because that would immediately make it obvious to those who don't follow the lore that Jaina's a fraud, and everyone in the Alliance is ignoring her bs because she's Alliance and they don't see her actions against the Horde as a bad thing, and everyone in the Horde is ignoring her bs because the Horde was crippled after SoO and would be incredibly foolish to bring it up with the Alliance looking for any reason to keep fighting and kill them, not that the Alliance wouldn't suffer a lot of casualties too.
Alliance say "the whole world will suffer" when talking about the Horde gaining power, but what they really mean is "the Alliance will suffer."
Like we humans say something like "global warming will be the end of the world" but it won't. It'll just be the end of us humans if plants die and we can't manage to adapt and survive.