So they came in their hundreds and thousands and marched. Nurses, firemen, pensioners, mothers with buggies, trade unionists, librarians and teachers among them. The March for the Alternative in London this weekend was the UK's biggest protest since the anti-Iraq war demonstration in 2003.
It was an old-fashioned spectacle with flags, banners, children and balloons, only slightly marred by pockets of violence and a sit-in at one of London's swankiest department stores.
Truly there was no Tahrir Square in Trafalgar, and those who claimed there might be only looked the more ridiculous for saying so.
Union leaders hoped 100,000 people might take to the streets of Westminster on Saturday to protest against cuts in government spending. In fact, there could easily have been more than 250,000, and organisers claimed 400,000.
The left must have been heartily relieved at the display, for considerable political credibility was invested in the march.
The British coalition government may not be popular, but as the weeks go by its key players are looking more assured and confident of their strategies and have the external plaudits, from the Organisation for Economic Co-operation and Development and the IMF, to prove it.
If the opposition is not yet in crisis, it has looked pallid. Ed Miliband has not proved to be a charismatic leader of the Labour Party, and his lacklustre shadow cabinet appears incapable of suggesting real alternatives to the government's economic policies.
It would be crediting the union movement with too much influence to suggest it has stepped into the breach - it certainly has not. But with this march, the union movement at least appears to have captured the popular imagination.
Mr Miliband's decision to address the marchers was a gamble. After all, the Labour Party manifesto also pledged to cut back public spending to help reduce the deficit. But this weekend the opposition leader helped to shore up his own support, with his message that cuts have gone "too far, too fast".
However, when the images of Saturday's march and the euphoria of collective protest have faded, a problem remains.
What is the alternative for which so many have so blithely marched?
An alternative is surely another path, a different way, a choice. But Labour has no alternative idea to offer.
For sure, there were some platitudes about Robin Hood taxes - making bankers pay - cutting tax avoidance, making the rich pay more and saving public -ector jobs.
But however many people march, they are not going to convince the government to go back on its plan to curb public spending and eliminate the structural budget deficit by 2015-2016.
And while some of the cuts will be harsh, they will return public spending only to the share of GDP that it was in 2004.
The office for budget responsibility, which keeps a watchful eye on the government's forecasts, says that by the end of this parliament, the chancellor will still be spending £100 billion (Dh589.25bn) a year more than the level he inherited.
It is all a bit too late really. This is an argument that should have been made and won last May, when the general election was held.
The union movement is mobilising itself now because public-sector workers are just beginning to lose their jobs.
It was two years ago that workers in the private sector were hit. Some of the UK's biggest employers laid off thousands of people, and those who remained in work suffered indefinite pay freezes.
The sad fact is that the state became too big under Labour. Too many people were dependent on working for the state or for quangos that were wholly dependent on it. The evidence was there on Saturday.The state's net has caught up many people, including the higher-rate tax payers who pocket subsidies for their child-care and the pensioners who receive winter fuel payments in their Spanish homes.
Inflation will make it harder for the government to impose the spending cuts that have been decreed necessary, but that means it is all the more important for the money that is spent to get to those who need it.
There was another complaint heard again and again from the weekend marchers: "We didn't create this mess, why should we pay?"
But neither did their children or their grandchildren. So what is the alternative?