Jon Stewart on Monday revisited Occupy Wall Street, surprised that protests have spread to dozens of U.S. cities and abroad.

"They're like the Hard Rock Cafe of leftist movements," Stewart said.

But the image of a protester defecating on a police car troubled Stewart. "No!" he said. "Naughty. Here's the problem. Unfortunately, protests are often as much about optics as they are about substance.

"You have tapped into a real injustice that people feel about the global financial markets," Stewart continued. "Nothing can derail your movement faster than someone who is unable to derail their movements."