If you bury your head in the sand and pretend that people will never break the social contract because "inequality doesn't matter" and "macroeconomic indicators look fine", you're going to miss a big part of the picture.
[0] http://www.politico.com/magazine/story/2014/06/the-pitchfork...
The question of "Why not just kill the people who have what you want?" is fundamentally a dystopian one. Feudalism, warlords, not a way to move forward. There are plenty of examples in the world today, just look at Syria which has millions of people who could be productively running shops, writing books, learning about the world, developing new products, and instead they displaced in refugee camps in Turkey by war between fundamentally ideologically disjoint groups.
So while it may be uncharitable to suggest someone seek psychological help for asking the question, the fact that the question is even considered as a possible "solution" (and it is presented that way in the GP post) raises a bigger question which is "What exactly does the poster expect to be the result of people just going out and killing other people they don't like?"
> I'd probably tear up the person with the bag
"I would literally murder a random innocent" is a bit different from what you suggest.
Where on earth did you pull this dichotomy from?
Essentially, morality and right/wrong are seen as "relative". Thus, you get situations where basic, very simple morals are thrown out the window by some sort of superseding narrative. Unfortunately, we're conditioned into it every day. Long story short: "it's okay to do bad things to bad people" is glorified and romanticized. While the opposite, absolute moral of "doing bad things is bad" is ignored.
It's hard to not take this sort of discussion into the realm of politics. But, again, long story short: If we were ever to use absolute morals, we'd very quickly run into a slew of problems with most political systems every created or envisioned.
littletimmy's comment was a good occasion to apply the Principle of Charity: http://philosophy.lander.edu/oriental/charity.html. An easy plausible interpretation was that he was asking why violence doesn't happen more often—not advocating it.