It has been a long time coming. Four decades have passed since James Tobin, a Nobel-prizewinning US economist, first proposed "throwing sand in the wheels" of the financial markets by imposing a tax on transactions. Now the idea is within months of becoming a reality.

The European commission has given the green light for a eurozone "coalition of the willing" to go ahead with a financial transaction tax (FTT), likely to be levied at 0.1% on shares and bonds, and at 0.01% on derivatives.

For its supporters, a transaction tax is a classic no-brainer: it will punish those who plunged the world economy into its deepest slump since the 1990s and raise lots of cash from banks, cash that would otherwise have to be extracted from blameless members of the public. Many countries already have taxes on financial transactions (stamp duty, in Britain's case), so this is hardly a revolutionary proposal.

Opponents say that it will add to the problems of the financial sector when it is already on its knees, raising the costs of funding and so leading to even weaker flows of credit to households and businesses; the fact that the FTT is not being universally levied, even within the eurozone, means it will be simple to avoid the tax; Frankfurt's loss will be the City of London's gain, because the UK's position is that an FTT has to be imposed everywhere if it is to work.

The likelihood is that the FTT, in its current form at least, will neither be the magic bullet claimed by its supporters nor the wrecking ball claimed by its detractors: it is too small to "throw sand in the wheels" (Tobin's original plan was for a much heftier tax). If it does succeed in reducing churn in financial markets, it won't raise the sums expected by the 10 countries involved.

On the other hand, the idea that the FTT is going to be the final straw for the financial sector also looks well wide of the mark. In the light of what has happened over the past five years, a transaction tax is going to be well down the list of worries for Europe's banks. Avoiding paying it could prove to be more trouble than it is worth.

Both sides of the argument should, however, welcome the arrival of the FTT. Why? Because we will soon know who is right and who is wrong. A tax that includes the four leading economies of the eurozone – Germany, France, Italy and Spain – is big enough for the results to carry significance.

We are about to witness a controlled experiment that the rest of the world will be watching with some interest. If the FTT does generate billions of euros in extra revenue for Angela Merkel and François Hollande, other countries will be quick to seek a piece of the action. If it doesn't, the idea will die a quick death.