The premise of democratic socialism is not that market economics must end but that the market is not the end. Rather, it is a means to serve collective human ends. The market is a technology that, like any other technology, must be controlled by human agency. Even in capitalism, notwithstanding the ideology of free market fundamentalism, the market turns out to be a means, too — for the concentration of wealth and power. In socialism, by contrast, the end is a universally shared distribution of wealth and power, which requires a distinction between those who profit most in the market and those who determine the rules governing society. Without such a check on power, the market technology becomes a weapon by which the prevailing few oppress the rest.
In the United States, such a distinction has nominally existed because in theory most citizens are free to vote for representatives who are not necessarily beholden to concentrated wealth, at least since political rights expanded beyond propertied white men and until Trump dispensed with the pretense of a separation between political rule and personal profit. But even during this apparent interregnum, the holders of concentrated wealth wielded the power they had accumulated from a history of dominance to make democratic control over society merely a formality, through a wide variety of underhanded tactics including but by no means limited to the repression of socialist ideas, the disenfranchisement of African Americans, and the financing of political campaigns.