One does not have to be a Marxist or other variety of radical to acknowledge basic differences and fundamental conflicts between these falsely conflated phenomena. Survival of the fittest' and inequalities in purchasing power are what capitalist efficiency is all about.
Individual profit comes first and firms become efficient to be rich.
Democracy is not. But democracy's priorities are equality before the law, the right of each citizen to govern the decisions that govern his or her life, the creation of a civilization based on fairness and equity. Capitalism's priorities are inequality of return, profit for the suppliers of capital, efficiency of production and distribution, the bottom line. There is plenty to criticize from a radical perspective in Thurow's and Longworth's more extensive formulations on the question. The great western conflation of democracy with capitalism originated with the crisis of European feudalism and the great European and North American bourgeois revolutions of the 17th to l9th centuries.