It comes down to this: if you think that economics is a zero-sum game, then yes, it is unjust. First world consumption comes at the expense of the poor elsewhere, the rich are leeches sucking money from the rest of the economy, and 35 hour work weeks create jobs.
Good news is all signs point to economics not being a zero-sum game, and thus most of the responses you are getting are likely correct - your premise is flawed.
Claiming that anyone discussing inequality is implying economics is a zero-sum game is making a strawman argument.
There is a continuum between two extremes - at one extreme, you have a zero sum relationship, where the total output (as measured by some sensible metric) is capped and it gets divided up, through to a view where there are unlimited resources and no constraints on growth, and the activities of people are synergistic but not competitive.
Both ends of the continuum are easily shown to be fallacious, but your argument only holds if you assume the unlimited resource end of the continuum is true.
The reality is that there are finite resources, and physical, biological and sociological limits how fast and efficiently they can be sustainably exploited. That said, there is clearly a lot of room for improvement in how efficiently we use resources - as many Internet startups are doing - as well as how sustainably we use them.
There is a problem with rich people consuming things that drive poor people into unacceptable employment to provide raw materials for those things.
Materials like gold, or minerals for tech, are often mined in ways that most people would find appalling.
People have a perception of "fairness" and a big tech company making millions, billions of dollars of profit while people are mining minerals in dangerous conditions for very little money is seen as unjust.
For someone getting $2 a small amount of money, just 50c, is a huge raise, and it would have little impact on the end price of the goods.
Quite small amounts of carefully targeted money could make a big difference to developing nations - better schools, clean water, better medicine, etc.
It would be really nice to see tech companies devoting a bit of time and smarts (and maybe even a bit of cash) to tackling those problems.
Good news is all signs point to economics not being a zero-sum game, and thus most of the responses you are getting are likely correct - your premise is flawed.