So, the Daily Telegraph is so upset at Lib Dems thwarting their rightwing dreams that it launches a dubious sting operation against ministers. Hooray! Vince Cable, Steve Webb, Michael Moore and Ed Davey duly reveal that dealing with Tories sometimes requires them to hold their noses and that they dislike some of the government's nastier, dafter policies. Huzzah! And chief fall guy Cable admits, further, that he thinks Rupert Murdoch's attempts to expand his media empire still further are pernicious. Alleluia!

Of course, Cable does not come out smelling of roses and Julian Glover makes some valid points about his personal weaknesses. But do these revelations show the Liberal Democrats to be unworthy of their seat in government? No. The chief problem with this government – most keenly felt by Lib Dems – is that it has failed to demonstrate to the public, media, or even itself, what coalition government means.

It has till now succeeded, to a quite extraordinary degree, in showing that two parties can work together for the greater good. But it has not been able to show that the two parties remain ideologically distinct rivals. Compromise and cabinet responsibility are, of course, essential in coalition – and a sign of mature politics. But they come after long, hard arguments. Webb was spot-on in suggesting that the public impression was of a far too cosy arrangement .

Until they were entrapped, Lib Dems had shown remarkable restraint in holding their tongues over terrible policy decisions, such as the cut to child benefit, which most of them opposed. Now voters can see at last what Lib Dems have really been up to in government. The media fantasy of a Clegg-Cameron love-in is shown to be utterly superficial, as Lib Dem supporters always knew it to be. Below the surface, Lib Dem ministers have been achieving progressive goals and fighting against regressive ones. They cannot always win, but thank goodness they are trying.

Careless or not, Cable was right to condemn the unnecessary and unaffordable actions of over-eager ministers like Michael Gove and Andrew Lansley. It is nonsense to introduce wholesale reforms in education and health without the resources to finance them. The Lib Dems are part of the government and must take responsibility for its bad decisions as well as its good ones. But it will do the party no harm to show a bit more often that it does know the difference.

It is more than the Labour party can manage. Just a week after offering constructive dialogue with Lib Dems on policy development, Ed Miliband has again shown weak political judgment in opportunistically attacking Cable. Which parts of Cable's objections to the Tories does he actually disagree with? Let's hope this is not yet another craven Labour attempt to appease Murdoch.

It will be a tragedy if Cable's undiplomatic leaks lead to approval of News Corporation's attempt to buy the remaining shares in BSkyB. Their influence over British politics may not be quite as great as Murdoch thinks it is – let's not forget that his hysterical support did not enable the Tories to win the election, despite Labour's manifest weaknesses. But over-concentration of power and influence is clearly bad for democracy. Indeed it is a key driver of political, social and economic inequality. No doubt rightwing Tories would be delighted to see the creation of a politically biased British equivalent of Fox News. As Will Hutton argues, it is a crying shame that Cable's indiscretion means he has missed the chance to stand up to them. But far bigger shame on Jeremy Hunt if he now waves the white flag at Murdoch.

At least Cable has shown he is brave enough to do battle with the rich and powerful. It is not easy and, with only seven months' experience in government, Lib Dems are bound to make some mistakes. But this whole affair has shown why progressives should be pleased that he is there.