Sorry, Sinrek! I misspelled in my haste.
I offer you my insight on what I think in deatail now however in exhange of your pardon for my previous mistake.
Here is the quest.
https://vanilla-twinhead.twinstar.cz/?quest=1195
If you look at it then you notice that it doesn't ask you to kill them. A blizzard employee decided to leave you with only that option and that is their method in most cases in this game. They don't follow the story entirelly, nor do they represent how it would play out in a real scinario and their methods are even more brutal at places than neccesairy. They manipulated its story to their liking and lost track of the nature of the lore. A tauren wouldn't ask you to kill for a mere phial according to their tale. Blizzard is a huge corporation afterall that runs on money and their sponsors evidently care more about productivity than credibility. It doesn't change the fact though that there are many in the horde who are savage in nature. The trolls lived as wild beasts. To them that had been considered life. The orcs even though once noble were manipulated to act vile. They lost their ansestral homeland where they lived in peace and harmony before Kil'Jaeden's planted the seeds of his evil scheme. Thus many of them fell afar from their old ways and turned to bloodrage. The Forsaken were simple peasants and merchants who lost their sanity after the cruel and to them at the time unthinkable plot of Kel'Thuzad and his cult of the damned's. As did the blood elves had after having laid their milennias long lasting majestic kingdom by the Scourge under Arthas' hands. It was only the tauren who had relative peace before these times who still have their homeland and weren't dealt such cruel fate as the other three.
So you could cut them some slack because they aren't innatively evil. Some are but that has been always the case. It is just a few that stirr things up and then the simple minded follow. As of now they wish to build such a society for the horde under the rule of Thrall and the alliance is by far from faults either. The human society is full of deceit and political plotting. The gnomes and dwarves tend to overexert nature's rescourses and they lay waste through their excavations and innovations and don't forget that it was the elves pride and reckless use of magic that brought Sargeras to Azeroth in the first place. Not to mention Malfurion's ignorant behaviour towards Illidan that eventually lead to so much chaos.
Every coin has two sides.
You know. In life you must find the ones you can trust. You can not trust or distrust anyone based on your predjudice for that might very well just differ from reality. Not all orcs are as Thrall, nor does Cairne trust the entire orcish society but he trusts Thrall and put his faith into him for he is strong and willing to discipline his people even with force if he deems neccesairy. So did Jaina. So did Grommash and Drek'Thar, Vol'jin. Fate is a mysterious thing that keeps changing our paths and you can only build your present if you keep your eyes open for if you feed from the past only then you might end up like Sylvanas whose zeal for revenge overshadowed her mind and sanity. Forgetting the really important aspects of life which is love, camaradiere and the like.
Explain it to me what was it that you found disturbing regarding Thralls decisions as he claimed Durotar for the orcs for I believe he had to act harshly even though I don't know the circumstances but I know that desperate means require desperate measures and that his intentions are of purity. However again. I don't know the details but if you wanna investigate it together then englighten me! I'd gladly accompany you on the journey.