Democracy- Good in Theory?

When discussing the relevance of Cummunism as a system of government, people almost always defer to the argument that Communism looked good on paper but has failed in reality. This argument has become so universally accepted that it has essentially discredited the viability of Communism as a legitimate form of government. My fear is that as the United States moves further from its roots in republicanism toward the instability of populism, democracy will go the way of Communism as a system that was good in theory, but that could simply not withstand the fleeting passions and misdirection of the masses that ran it into the ground.