Writing on the protests in Brazil recently, a New Yorker columnist posed the conundrum of "revolt in the midst of relative prosperity": "Since 2003, some 40 million Brazilians have joined the middle class … the protests have been widespread, popular and, most striking of all, dominated by the middle class." The explanation, he said, was that Brazil is a middle-class country with the infrastructure of a poor country.

This is not a new trope. According to the UN assistant secretary general, Heraldo Muñoz, a "new middle class" is responsible for a wave of protests across Latin America. Francis Fukuyama, seer of "the end of history", says we're in the middle of a global middle-class revolution. This analysis suggests that protest arises from the thwarted aspirations of a thrusting new petty bourgeoisie. The UN says a member of the new global middle class earns between $10 and $100 a day, and thus has spare income for consumption. On this basis, it estimates the middle class will grow from 1.8 billion in 2009 to 3.2 billion in 2020.

The Financial Times explains: "With their basic needs mostly satisfied, they begin to look more widely ... these aims amount to a call for the development of fully functioning democracies, with the rule of law, financial transparency and respect for minority rights."

This is reheated Fukuyama-ism. The "end of history" thesis was that after the cold war, liberal capitalism no longer faced serious competition. This analysis interprets the protests as a middle-class attempt to expand and deepen liberal capitalism. Whereas some people detected a challenge to the post-1989 consensus in the Arab spring, these analysts find only its further confirmation.

There is a novelty here. In traditional mainstream social theory, the middle class was a bulwark of stability, neutralising the antagonism between workers and capitalists. Through social mobility, it would dissolve both antagonistic classes into a common stew, ending class as such. In short, the middle class was a class-of-no-class. When Tony Blair declared the class war over, it was linked to his conception of a largely middle-class society. Now, far from being a factor in cohesion, the middle class is "revolutionary". Only, the limit of its revolutionary ambition is the deepening and consolidation of a neoliberal consensus.

In a weird inversion, this same analysis is also used to delegitimise protests, to link protesters to a global elite of Soros-funded, iPad-thumbing liberals with no concern for the poor. Yet both versions of the theory essentially agree that the poor and the traditional working class can play no significant historical role any more, except perhaps as passive support for corrupt and reactionary regimes, or their smartphone-wielding opponents.

There are a number of problems with this type of analysis. First, the "middle class" at the heart of this triumphalist ideology doesn't look like a class. To be able to consume more than one strictly needs is nothing special. To make it contingent on a certain income bracket is arbitrary. In the postwar era, workers were said to become "embourgoised" when they had cars, washing machines and holidays in Margate. In today's capitalism, $10 a day is sufficient.

The deeper problem, however, is how this conception implicitly defines an arbitrary baseline of "need" above which any other consumption is a "middle-class" bonus. There is no such thing as needs that aren't to some degree relative, or socially constructed.

And is the implication that anyone on more than $100 a day is "upper class"? Baby Cambridge wouldn't get out of his cot for $100 a day.

Further, note how vapid the argument is. Poor people protest because they don't have stuff, and want stuff. Middle-class people protest because now that they have stuff, they want different, less tangible stuff. This does nothing but skate on the surface of events.

Finally, it is just wrong about the details of recent uprisings. South Africa's rebellion against police brutality is driven by a labour movement whose members were gunned down by police in the worst massacre since Sharpeville. In Egypt, no revolution was possible without the Mahalla strikes and the rise of organised labour. In Latin America, from Argentina to Brazil to Bolivia, democratic movements have been driven by the poor.

Paul Mason has documented the surging growth of the working class south of the equator. These are workers whose only asset is their labour power, which they sell in order to survive. Profit, the final, directive purpose of global production, depends on their doing so. This gives workers potential power.

This is not to deny a pivotal middle-class role in the revolts. But we need to understand the middle class better to grasp its contribution. The middle class historically consisted of small traders and professionals. In the 20th century this layer contracted, and a "new middle class" emerged, consisting of middle managers and supervisors, and an expanded layer of state employees who were neither in command nor completely subordinate. They exercised more autonomy and social power than most workers, yet this autonomy and power was delegated by those in charge. What these layers bring to a protest movement is money, connections and cultural capital. They are more educated, have better use of technology, and are less likely to be ignored by the media.

For all this, we are not simply seeing "middle-class revolutions". While workers have not led these global movements politically, they have added critical momentum and muscle – in Egypt, in Turkey, and in Brazil. Even in Bulgaria's complex uprising against austerity, privatisation and corruption, the threat of labour action makes a difference.

In these rebellions, the working class has entered a broad, popular alliance not as a passive support but as a potentially powerful factor, with its own interests. The pundits overlooking this largely didn't anticipate the events of 2011. There are likely more surprises in store for them.