The leaders and backers of the Yanukovych regime in Ukraine and the Maduro regime in Venezuela have had a ready answer. The demonstrators are fascists, neo-Nazis and criminals.
Russian President Vladimir Putin's sidekick, Prime Minister Dmitry Medvedev, called the demonstrators "masked and armed people" with "black masks and Kalashnikov rifles" using "terrorist methods."
Backers of the Venezuelan regime, headed by Hugo Chavez's chosen successor, Nicolas Maduro, say that the street demonstrators are selfish rich people and fascists trying to launch a coup d'etat.
Others see the crowds differently. Timothy Snyder and Anne Applebaum, distinguished historians of Eastern European, stress that the Ukrainian protesters include Russian as well as Ukrainian speakers, people on the political Left as well as the Right, Christians and Jews and Crimean Tatars.
In Venezuela, the New York Times reports, protesters include many with modest incomes, frustrated with horrific violent-crime rates, people worried not about investment portfolios, but about shortages of milk and toilet paper.
From a distance, it's impossible to gauge the motives and backgrounds of all the protesters, and surely there are among them some whom almost all Americans would consider repugnant.
But it's noteworthy that they are taking grave risks -- dozens died in Kiev's Maidan Nezalezhnosti and many have died in Venezuela cities -- to oppose governments with roots in the political Left.
The protests against Yanukovych began when he shifted away from the European Union and toward Russia's Vladimir Putin, who characterized the dissolution of the Soviet empire as the greatest tragedy of the 20th century (a title for which there is vigorous competition).
In Venezuela, Chavez and Maduro embraced socialism, with the state taking over oil operations and revenues, and vigorously proclaimed their support for Fidel and Raul Castro's Communist Cuba.
American mainstream media, nostalgic for Vietnam War protests, tend to regard protests as the province of the political Left.
They hailed the Occupy Wall Street encampments, despite their violent crime and gauzy pronouncements, as heralding an uprising of the virtuous 99 percent.