A rebel fighter walks in a devastated alley of Aleppo's old market, in the UNESCO-listed northern Syrian city on February 27, 2014. Some 3,300 people have been killed in fighting between rebels seeking President Bashar al-Assad's ouster and their erstwhile jihadist allies since clashes erupted in January, a monitoring group said on february 26, 2014. AFP PHOTO / AMC / ZEIN AL-RIFAI (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)

DAMASCUS, Syria -- Mosab Khalaf remembers the exact moment when he became a revolutionary, and the exact moment when he walked away.

The first came early in the Syrian uprising, in the spring of 2011, when a friend dragged Khalaf, then 19, to a protest in Attal, a town in suburban Damascus. When he arrived, Khalaf was stunned by what he saw.

Near the central town square, security forces dressed in full combat gear had begun to descend on a crowd of several hundred demonstrators, who were marching with flags and chanting anti-government slogans. Khalaf watched as some of the officers grabbed hold of an elderly man, who had fallen behind the retreating protesters, and dragged him back across the square, beating him along the way.

“They were like monsters,” he said. “They were punching him, and he tripped and fell on the ground, and so they started kicking him, yelling at him, ‘Stand up!’ But of course he couldn’t stand up. He tried to, and they would kick him again.”

By the time the officers had dragged the old man back to their vehicles, his face was disfigured and bruised. “You couldn’t even see his eyes,” Khalaf recalled. “I'll never forget what I saw."

The second pivotal moment for Khalaf came a few months later, as the peaceful uprising began to lose momentum and some protesters started taking up weapons against government attacks. Khalaf had become a dedicated protester and organizer, driven by the realization, he said, that "everything I knew about the regime was a big lie." But he strongly discouraged his friends from letting their cause become a military one or joining the nascent Free Syrian Army.

Over the course of two days in the fall, as the fight grew increasingly violent, his worst fears came true: Two of those friends were killed. The first died when a regime missile landed on his home in a Damascus suburb; the second was killed by a mortar fired by rebel fighters.

“I stopped at that point,” Khalaf said. “I was lucky. I was able to stop, to become more logical. But my friends, they drowned in their emotions."

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The Syrian uprising, now in its fourth year, has tested and divided the many activists who joined the revolt. It has forced people who agree on one basic tenet -- that the government of President Bashar Assad is restrictive, authoritarian and cruel -- to make countless hard decisions: whether to take up arms or to remain peaceful; to embrace the extremist rebels, who have proven to be among the best fighters, or to support only more moderate opposition groups; to remain in the country or to leave.

Among opposition supporters in Damascus, where the threat of warfare looms daily, it is this final divide that resonates most powerfully. And it tends to presage an even more painful reckoning: whether, in the face of the deep-rooted obstacles before the revolution and the rising tide of violence, the opposition should continue the fight wherever it leads, or whether they should pursue some sort of mediated solution.

Last spring, a popular and widely followed activist blogger from Aleppo, who writes under the pseudonym Edward Dark, published an essay in which he concluded that the opposition had already "lost the Syrian revolution" once they made room for armed, extremist rebels to take power.

"It was around about that time that I gave up on the revolution, such as it had become," he wrote, "and saw that the only way to Syria’s salvation was through reconciliation and a renunciation of violence."

Not everyone who left the country still supports the revolution, and not everyone who stayed behind has turned against it. Especially in the besieged and bombarded rebel-held areas, many Syrians consider the actions of the regime over the past few years, and the more than 100,000 lives lost, to be unpardonable and unforgettable.

But Dark has been joined by a growing number of young opposition figures who, like Khalaf, have remained in the country, where they feel the impact of the war's fury on a daily basis. They draw a simple, if gravely disappointing, conclusion: Even if it undermines the revolution, the war must end.

"I don't love this regime, because it's killing the people, but this has been enough," said one Damascus resident, who formerly championed the protest movement but has since turned away. He spoke on the condition of anonymity to discuss his activist past. "For me, at any price, I want this thing stopped. I don't care if Assad stays in power, but I don't want blood anymore."

Khalaf is now 22 years old, with a sleek face, a puff of curly brown hair atop his head and a strong air of self-assurance. On a warm afternoon in March, he was sitting on a couch in the offices of the political opposition group he works for, Building the Syrian State, and surfing Facebook on his laptop.

Building the Syrian State was founded in the fall of 2011 by Louay Hussein, an Alawite Muslim who spent seven years in prison in the 1980s for his political activities, but nevertheless remains dogged by charges that he is too close to the Assad regime.

The very existence of an organization like BSS, which pushes for a sort of political reform from within but doesn't embrace the more decisive ambitions of the uprising, is often viewed warily by Syria's diehard revolutionary activists. They see it as lending undue credibility to the regime by providing the appearance of a functional political opposition, rather than creating an incentive for the government to change.

Anas Joudeh, the group's vice president, acknowledges this is a sensitive matter. "We're not naive," he said. "We know the regime uses the fact that we're here to give it legitimacy. But should we just go home because of that? No, we should use this small margin of space we have and try to make it larger."

Khalaf endures similar criticism from former friends and allies in the cause, many of whom now live abroad and accuse him of having betrayed the revolution. But he said he doesn't worry about their complaints.

"They can say what they want," he said with a wave of his hand. "They are not here. They are not suffering from the consequences of this war."

Across from Khalaf sat Khaled Harbash, another young BSS member with a similar history during the uprising: In early 2011, Harbash helped lead the nonviolent protest movement in Hama, a northern city that was once the heart of Syria's revolution. But as the regime responded to the demonstrations there with brutal force, and members of his group broke off to join the Free Syrian Army, Harbash found himself drifting away.

"After that, I didn't want to be in the revolution anymore," he said. "Because it wasn't a revolution, it was a war. There were no strikes, no other activities that made you feel like you are in a revolution. And for me, a revolution needs politics."

Khalaf and Harbash insist they haven't renounced the philosophical underpinnings of the revolution -- the grievances that drove them to the streets in the first place. They are careful to emphasize that they don't condemn their friends who eventually chose to arm themselves. They just think the decision to take up arms was a mistake that has led the revolution fatally astray. "I am still fighting, but in my own way," Harbash said.