I readily admit that I have never had a lot of time for Iain Duncan Smith, and doubt I ever will. But his Marr interview yesterday about the reasons for his resignation struck me as surprisingly sincere. I do think he resigned because a line had been crossed by George Osborne and Duncan Smith could not concur with his having done so. As someone who has resigned from jobs in the past on points of principle I recognised in what Duncan Smith said something that I have felt in my time: that a point can be reached where it's not just that all the other petty irritations of many working relationships become paramount, but that they are actually insignificant because on affront to what the person resigning thinks themselves to be has arisen and there is no likelihood of reconciliation on that point arising. The time to go has been reached.

I realise that there is much discussion on the impact of many other political events on this resignation. And I am all too well aware that it seems odd that after six years of attacks on the least well off in our communities Duncan Smith thinks now is the time to act. But I believe him nonetheless; I think in his own mind he is being sincere and that a personal Rubicon, pitched at a place many of us might feel incomprehensible, was crossed and he felt he had to go.

That, though, is significant, for three reasons. First, it reveals that there is a callousness in the heart of the policy that has been pursued. I am fairly sure that it is the indifference of the Treasury that has eventually got to IDS. He has toed the line, delivered the excuses, compromised for the Party, defended as required by collective responsibility for just so long, and then cutting capital gains tax and corporation tax whilst hitting those on social security yet again finally became a slap too far, as of course it was.

Second, if Duncan Smith can feel this he is not alone. Others can too. And, just as after Geoffrey Howe's attack on Thatcher she was never able to deliver the dry justification for her own mauling of people in pursuit of the self interest of a few again so too might this be true on this occasion: IDS's resignation may deny forever the possibility of the likes of Nicky Morgan on Question Time arguing that benefits cuts and tax cuts being wholly unrelated events when every single person knew that was not true. The IDS legacy may make it impossible to compartmentalise these issues in the way that this government and the last tried to do for far too long.

Third, in that case the opportunity for new debate is opened up. It can now be said that benefit cuts have gone too far. And it should be said, just as strongly, that tax cuts have gone too far as well. The need for rebalancing: for seeking redistribution and not increasing inequality should surely now be on the agenda. And with it more radical reforms, like a citizen's income that is really designed to be simple, save admin cost, deliver universality, beat poverty, support pensioners, provide both opportunity and a safety net for those seeking to work on their own and that ensures no child needs to live in real need.

Iain Duncan Smith may have appeared to attack George Osborne but he did something much more than that. He attacked an ideology built on indifference that was intended to impose hardship. George Osborne may well have been consigned to political history. It's more important that the ideology is as well.