Even those in what remains of America's radical left don't make this argument (the few that do aren't taken seriously by their fellow leftists anymore); even in Europe, which is far more generous in terms of social welfare provision has
some level of wealth inequality. So it's definitely a huge strawman. PG makes several statements which shows that he understands important parts of the problem (poverty, mobility), but it's incomplete (and credit to him for writing a thoughtful piece on the issue - more people in power should be doing the same.) Instead, the picture looks more like this:
1) Massive wealth inequality distorts policies towards the preferences of the rich (http://faculty.wcas.northwestern.edu/~jnd260/cab/CAB2012%20-..., http://www.demos.org/stacked-deck-how-dominance-politics-aff..., Affluence and Influence), so reducing inequality does more than just give people more mobility; it allows government to more accurately reflect the will of the people. It's democracy-enabling. Massive inequality in wealth breeds massive inequality in political power. No amount of mobility or opportunity can fix this one, only inequality reduction itself.
2) As Hayes discusses in "Twilight of the Elites", we've learned that basically everyone in the US has accepted the current notions of meritocracy, social mobility, and equality of opportunity. What is currently not well-accepted is that in order to achieve anything like equality of opportunity and social mobility, you need more equality of outcome in the first place. One can express this as "reducing poverty", but that's just a _reframing the same idea_. We are in fact talking about redistributing money from the very rich and giving it to the not-rich, one way or another, to improve EoOpp and SM. That reduces inequality by definition.
3) Massive inequality itself increases social distance, which is partially reflected in #1. When all one sees, knows, meets, etc. are other wealthy people, one may wind up becoming disconnected from the plight of the non-wealthy. They become an annoyance, invisible, or irrelevant, which is reflected not only in policy, but also in self-reinforcing cycles of disinterest and disconnection in the realm of social relations. Inequality has to be reduced somewhat to reduce that social distance.
4) When we speak of inequality reduction, it can be understood as "wealth range compression." The top go down, the bottom go up. Many analogize chopping off the top and putting it at the bottom, but the compression metaphor works better IMO.
5) Some worry (like Acemoglu) that US inequality subsidizes other nations in terms of innovation. I think Edsall and others have completely demolished the argument, and its was largely facile in the face of facts like Sweden having invented the ultrasound, the pacemaker, and AIS (an advancement of GPS) or Denmark having invented the loudspeaker, Bluetooth, and Insulin. You could even argue the opposite: a society that gives people a better safety net (Peltzman effect again) combined with an entrepreneurial culture will produce more, not less innovation.
The recommendations for remedying this are fairly tame in the European / Scand. context, mostly because fewer of them have internalized ideas like "taxation is theft" or "everything that happens to you is your own fault." We should regard the following as non-controversial (some a restatement of your list items):
- Marginal tax rates at the top of 50% (France is even higher and still has rich people) and policies to make sure the rates stay progressive.
- Closing tax loopholes, forcible repatriation of stashed offshore assets, fully funding the IRS, and eliminating (for real) tax havens and their usage.
- Debt-free higher ed (full rides, living stipends, the works)
- A real universal health system
- No games with inheritance taxes
- Non-punitive, non-humiliating policies to help the poor like a GBI or expanded automatic welfare provision
- Not gutting social security
If we were to implement the whole of Sanders' platform, for example (most of which I agree with, a few items I think are questionable), we'd still be to the right of a Denmark or Sweden(!) We'd be slightly to the right of what we had during the Great Society.
It's a return to sanity, basic living standards, and mobility. Hardly the stuff of Galtian nightmares.