The claim you can't 'get an ought from an is' can be explained like this:
In meta-ethics, the is-ought problem was articulated by David Hume, who noted that many writers make claims about what ought to be on the basis of statements about what is. Hume found that there seems to be a significant difference between descriptive statements (about what is) and prescriptive or normative statements (about what ought to be), and it is not obvious how we can get from making descriptive statements to prescriptive.
Hume was right about this. In essence I don't think you can work from observation of a situation (an 'is') and work out from it what ought to be done. There's a fault in that logical flow: but that's because I think there are ethics that define what ought to be. I'm well aware that some don't agree.
I can only assume that the Conservative Party is populated by such people. And it seems that the malaise is found elsewhere in politics as well.
Why? Because what we're seeing is a perverse logic in politics at this moment: the argument that because we had a financial crisis in banking (an 'is') that we ought to cut social care, pensions, the provision of social housing, health care, education and much more pervades almost universally.
That's illogical. More than that: it's wrong. The fact that the Tories are finding it almost impossible, already, to deliver on almost any of their promises suggests that there is not only logical error in this basis of policy creation, there is practical difficulty too.
The simple fact is that health care needs in our society were not set by the scale of bank lending. And education needs exist, just as the disabled need provision and the elderly must live in dignity whatever the level of profit from financial speculation. Those things ought to happen because we are compassionate and do not wish others to suffer, because we care for future generations, because we do not wish people to live with disadvantage and because deep down we all fear poverty and wish to protect our fellow human beings from its consequence. Where that concern comes from need not worry us: it seems universal across faiths and between those of faith and no faith.
But if that is true then the political ramification of this error are huge. It explains the problem that our politics is facing. Across the political spectrum the argument that we must cut the deficit by cutting government spending on essential services has no ethic or logic behind it: it is a simple an 'ought' incorrectly derived from an 'is' and an unrelated 'is' at that. It is an argument presented as fact when there are ethical and practical alternatives: alternatives most politicians so far turn a blind eye too.
Hardly surprisingly the bankruptcy of policies based on this ethical error is becoming all too apparent, and remarkably quickly. And equally unsurprisingly, people are rejecting those policies precisely becasue they realise that their fundamental values are threatened by the amorality of the Conservatives' actions. That would have been true if Labour had done the same thing I might add.
The reality is this: there are ethics in our society. And there are real needs. And we expect government to reflect and act on them. At the last election none of the three major parties did that. No wonder politics is not gripping the imagination. People want, even if I readily accept they aren't all saying it, a politics based on 'ought' which then gives rise to 'is'.
We deserve nothing less.
When we get it, and only then, will we revive our society, big, small and diverse as it is, and our politics with it.