The clamour for a change in Labour's economic stance that began with In The Black Labour is now growing daily. Ed Miliband's speech today signalled that the change is underway. Many in and around the party will be cautiously relieved. Many others, however, will be deeply disappointed.

Commentators such as Mehdi Hasan and Polly Toynbee have demanded in recent days that Ed ignores the demands for a more clearly hawkish line. Instead, they urge, he should stand and fight for what he and they know is right and morally sound. Good economics makes good politics and, sooner or later, the electorate will realise that Labour was correct all along. They undoubtedly represent a very strong seam of belief within the party and wider movement.

But there are big problems with this 'stand and fight because we're right' position.

In the first place, it assumes parties win elections because they have a correct analysis and the soundest values. This would imply that the Conservative Party had the best policies for the eighteen years prior to 1997. A view to which Mehdi and Polly, I assume, do not subscribe.

It also overlooks the fact that every party and their supporters believes they are correct. We may caricature Tories or Lib Dems as ignorant or self-serving rather than sincere in their views but they think exactly the same about Labour. This reveals a fundamental truth about politics which is that the great majority of people just think they are right. Rational, evidence-based debate has only a limited impact, in part because it is very rarely conclusive. Assuming that the inherent rationalism and morality of our particular version of 'rightness' will win out is to flirt with a profound naiveté.

Indeed Labour's economic case is not nearly as self-evidently right as the 'stand and fight' brigade think it is. Yes, there is a good case to be made for a slower pace of deficit reduction or even a small stimulus as enshrined in Labour's five point plan. Wise men such as Martin Wolf, who hold no brief for Labour, have made the case many times. But arguing that a slower path to deficit reduction would be a wise policy is not the same as saying that our economic prayers would be answered by such a move. Inflation has been too high, productivity too low, investment too stagnant, global economic and political volatility too great for a small shift in fiscal policy to really blow away the storm clouds. In truth, Mehdi and Polly want to stand and fight, tooth and nail for something that would do some measure of good but probably not a great deal more than that.

What actually despatches governments is events not the right arguments. Most voters live their lives and ignore the detailed debates that occupy the political classes. It is usually only when something so big and bad happens that it cannot be ignored that voters think seriously about replacing the current lot with that other lot. That was the case with the Winter of Discontent before the 1979 election, the ERM crisis before the 1997 election and the banking crash before the 2010 election. A party in opposition has to rebuild its lost credibility in preparation for that moment. This is vital because, as the 1990 recession showed, a big event will not necessarily play for an opposition if they are not yet trusted to take over the reins of government. In short, a new opposition party needs honestly and painfully to understand why it lost the election and forensically address those failings not exclusively kick lumps out of the new government. Anyone who thinks this can be done without making an almighty effort to regain Labour's reputation for fiscal prudence and economic competence is buried far too snugly in their comfort zone.

Many will read this post and think it is simply arguing for Labour to roll over, adopt a Tory-lite position and hang patiently around until the voters get fed up with Cameron. That would be a misinterpretation. Opposition parties must stand and fight but they must make sure they have a chance of winning. Don't leap into the ring and start throwing punches if the referee (the media) and the ringside judges (the voters) have already decided you're a loser.

So support a slower pace of deficit reduction but don't make it the defining feature of the fight with the coalition. Instead use what few opportunities we have to persuade the ref and the judges that we're not quite as useless as they think we are. That must mean emphasising our commitment to tough-minded, fiscal practice, first and foremost.

Once that is established Labour might begin to get listened to on its wider message and where it might start landing blows on the government. Then it is time to start drawing the distinctions. Emphasise Labour's bolder policy for jobs and growth by using the power of the state to actively restore the competitiveness of British business rather than Osborne's reheated and chaotic Lawsonism. And, yes, talk about a vision for a fairer, more responsible capitalism but make it clear this is a vision for fairness within the context of austerity - a new type of social democracy for very different and difficult times.

Fortunately, this seems to be precisely the thinking behind Ed's speech this morning. There is much, much more to be done but, despite what the 'stand and fight' brigade might now say, the genuine fight-back may just have begun.

Adam Lent is co-author of In the Black Labour and formerly Head of Economics at the TUC. He can be followed on Twitter: @adamjlent.