The problem with this isn't just the obvious one, that we actually need more public spending and a looser fiscal policy than the Tories are offering. Even if we make the heroic assumption that Tory policy is right, the attacks on Labour are still horrible overstatements.
For them to be true requires some combination of two things to be the case: that slightly larger planned borrowing (the IFS thinks Labour's plans are for a bigger deficit of only around 1.5 per cent of GDP) will lead to big rises in interest rates; and/or that aggregate demand is highly interest-sensitive, so a rise in borrowing costs will choke off economic activity.
Neither of these is the case. Real long-term interest rates have trended downwards since the mid-90s, whilst government borrowing has increased. And if lower interest rates had a very powerful effect on spending, the economy would be booming now as never before.
Even if you believe that a looser fiscal policy would be wrong, it would surely not be a disaster. Not all policies that are sub-optimal are catastrophic. To pretend that they are is just stupid overstatement.
In one sense, such hyperbole is forgivable. One thing that all governments have in their favour is the fear of the unknown. It's natural for incumbents to play upon this by exaggerating the cost of the opposition's policies. And, of course, politicians are selected to over-estimate the good and evil that policies do: you don't go into politics unless you think policies make a big difference.
Nevertheless, such claims are misleading. It is, in truth, very difficult for governments in developed economies to make a decisive difference to economies or societies for good or ill. One reason why politicians are seen as useless is precisely because they cannot make as much difference to our lives as they pretend*.
A big reason for this is that economies are complex. On the downside, this means it is difficult for policies to have big, predictable positive transformative effects. On the upside, though, complex systems can be resilient to suboptimal policies and choices. As Adam Smith said, "there is a great deal of ruin in a nation." One of the under-rated differences between developed and under-developed nations is that the former are more resilient to shocks than the latter.
You might think I'm labouring the obvious here. Maybe. But maybe not. It's not just politicians who are selected to be biased to over-estimate the effects of policy. So too are political reporters. When they report hyperbole without giving it scrutiny they are promoting a false image of the economy - that it is a delicate flower vulnerable to small changes in policy. This is yet another way in which the media constructs a hyperreal economy which is unrelated to what the rest of us live in.
* I don't think the claim that austerity has depressed economic activity is a counter-example here. Fiscal multipliers, in bad times, are a little more than one. If they were 5, 10 or 20, austerity would be disastrous. As it is, it is just bad.