[dredmorbius]

"Rent seeking" would be a good description of what I had in mind, take a look at the Wikipedia article I mentioned.

Some financial activities -- traditional financing of productive economic activity with real returns -- actually generates productive financial and economic activity. Other forms of finance -- essentially create liquidity based on existing assets, but don't actually turn that liquidity into something productive. Say, roughly, a HELOC. Or they simply squeeze payments out of population that's poorly equipped to refuse them: fees, fines, and penalties added to many financial and services contracts.

I'd argue that both of the latter are "extractive" in that rather than promoting economic activity, they serve to convert some illiquid asset class (or population) into a currency pump for the benefit of the financier.

I don't know if computerized trading falls into this model but I'm inclined to think it does, and would very much favor a transactions tax to put limits on this sort of activity. I suspect the bigger problem is that these systems are poorly understood and have very large downside potential through inadvertent (or deliberate) feedback loops. Think Flash Crash.