There can be no guarantee as to which forces will win out in Tehran. But those on the left who were hostile to the huge protests are in danger of lining up with those who want to crush the movement.
Scepticism is necessary every time the media extol what they claim to be democratic movements against unpleasant regimes. The cheerleaders for the occupation of Afghanistan, Iraq and Palestine have a nerve talking about democracy.
It is hardly surprising then that much of the left in Latin America and the Middle East was hostile to the huge demonstrations in Tehran against Mahmoud Ahmadinejad's government. The Iranian government has, after all, outraged the US with its support for Hezbollah in Lebanon, its hostility to Israel and its friendly relations with Hugo Chavez.
Yet the hostility to the demonstrations was seriously mistaken in this case. For all its religious rhetoric, the Iranian regime is a capitalist regime prepared to do deals with imperialism - as is shown by its support for the government of Nouri al-Maliki in Iraq.
Its origins lie in the form capitalist stabilisation took after the 1979 revolution against the Shah. Religious slogans provided a brief unitary focus for the different social forces involved. But a section of the middle class, allied with a layer of wealthy merchants and leading religious figures, was then able to use religious and anti-imperialist language to conceal its real aims as it bloodily crushed other social forces, including independent workers' organisations, ethnic minorities and left wing guerrilla organisations.
It established a set-up in which there were elections, but overall power lay with a non-elected supreme leader and "unsuitable" parliamentary candidates were prevented from standing.
But it was not only repression that provided stability for the regime. In the post-revolutionary period it was able to provide certain important, if limited, reforms that benefited significant layers of the population - something many sections of the defeated left failed to see.
However, the stability of any capitalist regime depends on reconciling differing interests within the ruling class while containing discontent among the mass of the population.
From the 1990s onwards this was increasingly difficult. Private disagreements within the ruling establishment turned into open debates during presidential campaigns. By this year's campaign the establishment could no longer prevent its internal disagreements drawing a vast number of people from outside its own narrow circles onto the streets.
If all that was involved was the division between the two ruling class groups, scepticism would be justified. But clashes within a ruling class have a potential to unleash movements none of its elements can control.
The new forces that take to the streets can be very confused about their goals. They come from different social milieus, with contradictory interests and aspirations. Talk of "people power" conceals the gap between those who toil for a livelihood and those who hope to gain new privileges from the turmoil.
Students frequently play a key role in providing the initial impetus to such movements. They are not a social class in their own right and can give expression to the wider desire for deep, but unspecified, change. Hence the role of students in the late 1960s or in the Tiananmen Square movement that shook China 20 years ago. But as the movement draws wider sections of exploited and oppressed people into action, the different class interests at work inevitably began to have an impact on the activists.
There is incipient political differentiation as some see the way forward through reliance on the reformist section of the ruling class, some through radical forms of minority direct action, and some through looking towards mass action by the workers, the peasants or the urban poor. Such differentiation characterised the movements of the 1960s and 1970s.
Iran can be no different. All sorts of political forces will be attempting to fish in the movement. Some will be dubious in the extreme. The most corrupt figures from the reform wing of the ruling class will try to manipulate activists, as will the CIA and exiled royalists.
But any cursory glance at what protesters say points to very different currents within the movement. There are activists who emphasise the similarities between their plight and that of the Palestinians of Gaza. There are groups of workers who have seen the forces of the state attack their strikes and independent unions. There are students who have faced imprisonment for expounding socialist ideas and reading Marxist works. There are intellectuals who see the great advances of the 1979 revolution strangled by corruption and repression.
There can never be a guarantee in advance as to which forces will win out in a great political and social upsurge. But socialists have a clear responsibility in such a situation. This is to provide solidarity and encouragement to those who want to lead the movement forward in a positive direction. It cannot be done by lining up with those who want to crush the movement.
Twenty years ago some of the left internationally did support the crushing of the Tiananmen movement by Deng Xiaoping.
That crushing enabled China's rulers to override all forms of popular resistance as they unleashed the most untrammelled form of capitalism. The crushing of the movement in Iran would not stop a similar logic of capitalism working itself out there. But it would make it much more difficult for popular forces to emerge to challenge that logic - under either wing of the ruling class.