Ilya Somin at the Volokh Conspiracy questions why socialism retains its appeal, despite obvious flaws in its theoretical assumptions. Somin references economist Bryan Caplain, who points out that socialism ignores basic human nature and offers poor incentives to work and produce. A number of communes here in America went defunct for that very reason – freeloading overtaxed the system.
The democratic socialist argument is an extension of the more general standard argument for democracy, which is part of its appeal. The main rationale for democracy is that it gives government strong incentives serve the interests of the people. The democratic socialist argument is that the economy should be controlled by a democratic government, because that will ensure that it will be structured to benefit the majority of voters rather than a small class of capitalists. Thus, the main shortcomings of democratic socialism are likely to be especially severe forms of the flaws of democracy as such. However, for reasons I discussed here, these problems are much more severe if the size and scope of government is large.
Giving control of the economy to the government may seem like a swell idea, because the government is supposed to represent the people. But when the majority of the people figure out that they can exert control of the government and the economy to take money from a wealthy minorty, you get problems. Wealthy people lose their incentive to produce, less wealthy people lose their incentive to produce, and the system collapses under its own weight. No matter how hard it tries, socialism cannot redefine human nature.