What fascinates me above all about economics is that you can take an idea like the equity-efficiency tradeoff (or top marginal tax rates, etc.) and find studies that are literally all over the map on it. Maybe someday we'll have enough experiential data to come down conclusively about inequality, but right now we're all just tossing around opinions.

I think that pretty much most of the data support the thesis that the current level of inequality is far too uneven. The one study cited in this piece that has data showing that inequality is good for growth was published in '08, ya know, right before the house of cards collapsed.

As for this:

High tax rates and large subsidies to the nonworking poor can “dampen incentives to work and invest,”...

That's not a data-driven judgement; it's moralizing, projecting based on what the authors think might happen in their own idealized version of how economics works. Homo economicus has been debunked in study after study. Only the most ideological conservatives still believe in it.