I think it may be as simple as this: The rentiers would prefer not to be euthanized. Under capitalism, the elite are those who own (or control) money. Their function is, in a broad sense, to provide liquidity. To the extent that pure money-holders facilitate production, it is because money serves as a coordination mechanism, bridging gaps — over time and especially with unknown or untrusted counterparties — that would otherwise prevent cooperation from taking place.  In a world where liquidity is abundant, this coordination function is evidently obsolete and can no longer be a source of authority or material rewards.
More concretely: It may well be true that markets for, say, mortgage-backed securities are more likely to behave erratically when interest rates are very low. But in a world of low interest rates, what function do those markets serve? Their supposed purpose is to make it easier for people to get home loans. But in a world of very low interest rates, loans are, by definition, easy to get. Again, with abundant liquidity, stocks may get bubbly. But in a world of abundant liquidity, what problem is the existence of stock markets solving? If anyone with a calling to run a business can readily start one with a loan, why support a special group of business owners? Yes, in a world where bearing risk is cheap, specialist risk-bearers are likely to go a bit nuts. But if risk is already cheap, why are we employing all these specialists?
The problem is, the liquidity specialists don’t want to go away. From finance’s point of view, permanently low interest rates are removing their economic reason for being — which they know eventually is likely to remove their power and privileges too. So we get all these arguments that boil down to: Money must be kept scarce so that the private money-sellers can stay in business.
It’s a bit like Dr. Benway in Naked Lunch:
“Now, boys, you won’t see this operation performed very often and there’s a reason for that…. You see it has absolutely no medical value. No one knows what the purpose of it originally was or if it had a purpose at all. Personally I think it was a pure artistic creation from the beginning.
“Just as a bull fighter with his skill and knowledge extricates himself from danger he has himself invoked, so in this operation the surgeon deliberately endangers his patient, and then, with incredible speed and celerity, rescues him from death at the last possible split second….Interestingly, Dr. Benway was worried about technological obsolescence too. “Soon we’ll be operating by remote control on patients we never see…. We’ll be nothing but button pushers,” etc. The Dr. Benways of finance like to fret about how robots will replace human labor. I wonder how much of that is a way of hiding from the knowledge that what cheap and abundant capital renders obsolete, is the capitalist?
EDIT: I'm really liking the idea of Larry Summers as Dr. Benway. It fits the way all the talk when he was being pushed for Fed chair was about how great he would be in a financial crisis. How would everyone known how smart he was -- how essential -- if he hadn't done so much to create a crisis to solve?
 Capital’s historic role as a facilitator of cooperation is clearly described in chapter 13 of Capital.