I don't automatically assume it's a problem, as so many people seem to. I don't assume that all economic inequality is the medieval type, where the rich are the winners of a zero sum game.The problem I see with growing income inequality is not the "inequality" part, it's the "growing" one.
From a purely mathematical point of view, in any economic climate there's some level of income inequality that's going to be economically optimal for whatever it is that we want to optimize about our economy (some combination of jobs, happiness, wealth, or whatever). This is trivially true, as zero income inequality is a really crappy situation by most realistic measures of economic health, as is ultimate income inequality (i.e. a small handful of people holding all the wealth). In between those extremes there's got to be some optimal distribution of wealth.
But when I see a march towards higher levels of inequality, I'm left to wonder whether there are actually any forces in play that will keep us anywhere near that optimum, or if we're just seeing a runaway "wealth begets wealth" situation, as folks like Mandelbrot have suggested. Sure, it could be the case that the changing technological climate means that the optimal level of inequality is going up, and we're actually keeping pace with that, but that's just a "could be", and I've never seen a particularly compelling argument that our economy should work more efficiently now at higher levels of income inequality than, say, twenty years ago. An argument that increasing income inequality is inevitable, or even that it's fair, is not an argument that it's economically helpful.
I completely agree with your thesis that technology is a perfectly valid reason for the growing gaps, FWIW, it's a pretty unassailable argument. But I don't agree that it's not cause for concern: we're sliding at an increasing pace down the slippery slope, and at the bottom is complete human level AI, where a vanishing percentage of humans have anything at all of value to offer to the economy. Are you really comfortable with the wealth distribution that's going to result from such a thing?
Personally (and this is quite controversial, I admit), I think that we have to start taking that inevitable outcome to heart, and realizing that the next 50 years should be a period where we move a lot closer to a full welfare state, with full acceptance of the fact that more and more of us will be at the unemployed and useless end of the spectrum as time goes on. Then again, an economy where humans are less useful than their machines, even as far as designing and running those machines, is a completely different world than we've ever considered before, so perhaps it's premature to even consider what that means...