As Paul Krugman notes, we know of specific policies (taxes, shareholder say on pay, etc.) to address inequality, but no one has cracked the secret to sustainable growth that raises all boats:

The usual answer to this is to point out that we don’t actually know much about how to produce rapid economic growth — conservatives may think they know (low taxes and all that), but there is no evidence to back up their certainty. And on the other hand, we know how to make a big difference to income distribution, especially how to reduce extreme poverty. So why not work on what we know, as at least part of our economic strategy?

He further notes that economic growth rates do not effect levels of child malnutrition, but inequality does:

But even this argument may be conceding too much. A new study finds that in poor and lower-middle-income countries, one of the most crucial aspects of well-being, child malnutrition, isn’t helped at all by faster growth:

………

Yes, rapid growth is good, but it doesn’t solve all problems even if you know how to make it happen, which you don’t.

We do know that the conservative prescriptions produce, inequality, speculation, bubbles, and panics.

The reason that we continue to hear these arguments is because it serves the rich and their lackeys, not because it has ever demonstrated that it has any relation to reality.