[D_Drake]

Problem is, that's exactly how the human brain interprets real-life people, too. You can call it the Monkeysphere or Dunbar's Number, but fact is that people are incapable of conceptualizing random strangers on anything like the same level as familiar people. It's the reason you have more emotional reaction to a package being delayed than you have to a suicide bombing in Afghanistan. It's a limitation of the human brain. Movies and games with collateral casualties reflect the way every single human being actually looks at the world; you just notice it because it's someone else's version of who's important and who isn't instead of your own.

[DanielStraight]

Consider these two statements:

What you would do for your closest friends, you should do for everyone.

What you wouldn't do to your closest friends, you shouldn't do to anyone.

Your post explains why the first doesn't work, but that has no bearing only the second.

I may not feel as strongly for random strangers as I do for my closest friends, but I still wouldn't kill or torture or otherwise dehumanize them.

[UnFleshedOne]

It is not a limitation as such. It is a feature. If that worked differently the very idea that unknown, but substantial number of people die every moment (say from accidents and natural causes, to avoid "how it would change humanity" arguments here) it would cripple every person into permanent and severe depression (for the lack of a better word). Imagine a close friend or a lover dying every second.