Why the upset with Gilgamesh killing Illya?

The scene in which Gilgamesh killed Illya in Fate/Stay Night: Unlimited Blade Works is a big reason that many fans (especially Illya's fans) hate Gil for. They say, "Gil's torturing and killing a little girl", "she had a rough life, was mentally unstable, so she deserved more sympathy", "Gil was torturing Heracles", blah blah blah.  Here's my rebuttal:

1. Illya acts like a little girl but she's 18.  (I clarified this because some people act as if killing a loli were worse than killing a normal-sized adult).  Her appearance may gain her more sympathy than other adults would, but her role in the HGW made it a fair game.  Some people think she's an "innocent little girl" but Illya is bloodthirsty "little girl" who's out for blood as much as any Fate/Zero Masters did. I don't care how Prisma Illya or Carnival Phantasm portrayed her. I'm sure she wouldn't spare anyone's life if she's having the upper hand. For example, in her words: “Berserker, I don’t care what you do with Saber and Rin. You can kill them or rape them”. In VN Bad End, she keeps Shirou barely alive just to physically torture him. But "it's ok because she had a bad life," right?  /s
2. Illya - like her mother - was created by the Einzbern to serve as the vessels in HGW - to die, even IF they won the War. There was no victory for them. Illya was programmed to self-destruct in a few years. Their fates were sealed from the moment they were born. 
3. HGW is a life-or-death battle. Regardless of Illya's appearance, the only thing that mattered is: Did she understand the implication (life-or-death) of participating in a HGW or not? Did she understand the rules of a HGW? Did she participate voluntarily? Illya definitely understood these things, which equate to full competence. 
4. Her being a loli doesn't mean that other participants should have yielded to her. If you're weaker, you'll lose. You can't go around whining, because you fight voluntarily. It's like you're playing at a casino but can't accept losses. It's like L vs. Light in Death Note: they knew what's at stake but they entered anyway, so could either of them complain about being killed by the other?  
5. Illya's past:  All Masters in the 4th and 5th HGWs felt compelled to enter the HGW one way or another. This isn't a competition of whose past is the worst (considering that characters like Kariya, Sakura and Rin have terrible pasts, too)!  While I feel sympathy for Illya's life and Kariya Matou's plight, I do not feel hate toward the characters that killed them.
6. The part where Gil ripped her heart out wasn't torture (like some people claim it was) since she's already dead. Gilgamesh could have done it while she's still having her final moment with Berserker but he waited till she's dead instead.  If any kind of killing where an opponent does not die instantly is torture (as some fans claim), then 99% of killings in anime are torture. 
7. It looks like some people want nothing less than an absolutely painless instant death for Illya. But there's no such thing as NOT suffering when being killed. If you want instant death, there's just 1 option: cutting their head off - which people will argue as being more cruel.
8. It's ridiculous that some fans go as far as saying that "Gil was torturing Heracles"!  Seriously? Gil was having a fair fight with Heracles. Gil just happened to be stronger. So be it.  Gil annihilated Iskandar and no one complains. Yet when a loli is involved, people seem to lose their minds.
9. Nobody owed anybody an honorable death in the HGW. Look at how the Masters killed each other!  Gil killed Iskandar, whom he actually liked and respected, in 1 stab in the stomach - which was respectful as far as killing goes - but Iskandar didn't die instantly. Does that mean that Gil was torturing him? No. (It's worth noting that Sella's and Illya's loyalty must have very much impressed Gilgamesh, because it's generally a big deal when he actually took hold of one of his weapons to kill a person instead of just launching them).

Overall, I have zero problem with Illya being killed by anyone. Because the moment she entered the HGW, she's a participant like everyone else. I don't give extra sympathy to other characters (some of whom had horrifying pasts, too), and neither to her.