Regulated markets in a capital-centric economy serve, in aggregate, the interests of those who control capital, and therefore also drift toward monopoly. Liberals either don't understand this or are simply being deceptive by promoting the continuation of capitalism.
Even highly socialist countries like Cuba found that introducing regulated markets was healthy for their economies. Now if 'those who control capital' are themselves a small minority of the overall population who act in concert - well, that's a financial monopoly, and of course there are ways to break up a financial monopoly of this nature, such as re-introducing Glass-Steagall provisions that separated commercial and investment banking, eliminating offshore and similar capital tax shelters, etc.
Note that if it is a state body that controls all the capital and hence controls economic decisions like infrastructure development, this isn't so different in practice from having a small group of financiers controlling all the capital - in both cases you have a centrally-planned economy controlled by a small cabal that puts their own interests ahead of everyone else's.
