When we discuss inequality, I think there are a lot of assumptions made that make it hard to really judge. For example, TFA trots out the high number of people on minimum wage, and the high percentage of people below the poverty line. This is misleading, because it misses out on some key ways that "capitalism raises all boats," which are tricky to measure.
Off the top of my head...
The first is the commodification of goods. Fifty years ago, a washing machine, refrigerator, and color TV were high end, luxury goods, available only to the relatively wealthy. Living on minimum wage today, you likely have access to all of these things. Food, education, clothing, building materials, and luxuries are all cheaper (by hours of labor) than ever before.
The second is the quality of goods. That washing machine, fridge, and color TV that your local Best Buy employee uses are all unimaginably better than their equivalents 50 years ago. It's a washing machine with multiple programmable spin cycles. The fridge has controllable temperature, no freon, uses less energy, and is quieter. The color TV is a flat screen 42" with a remote control. This is also really hard to nail down, and it is a serious limitation for inflation measures, many of which are based on a fixed basket of goods - ignoring that the quality of a "raincoat" or "dental care" changes greatly over time.
The third is the invention of new goods. That person on minimum wage today also likely has Internet access, maybe even in their pocket. They have Netflix, GMaps, spreadsheets, online travel agents, and wikipedia. In concrete terms, this access to information and services is an infinite improvement over 30 years ago.
Finally, these comments ignore the historical context. Yes, some 12% of Americans are below the poverty line, and that's awful. 50 years ago, it was above 20%... and in the meantime, the population exploded. According to the US Census, the number of people below the poverty line has remained flat at about 40,000 since 1959, despite the population as a whole doubling in the same time. That's an amazing feat. It's terrible to have 12% of people in poverty - but let's not forget that we're moving in the right direction.
So, yes, it sucks that a lot of people are on minimum wage, and we should work to improve that. It's terrible that 12% of people in this country live in poverty. But the enormous improvement in what minimum wage MEANS in concrete terms, and the downward trend of extreme poverty, are largely due to the success of places like San Francisco. These measures are not the "dark side of capitalism" that TFA suggests.