We have presented to us a particularly stupid argument in favour of the building of the Swansea Lagoon:

A thousand high-value manufacturing jobs are set to be lost in the Midlands because of the government’s continuing failure to decide whether to support tidal lagoon marine power.

Two of GE’s British plants, at Rugby and at Stafford, had been designated to construct the underwater turbines and to provide the complex electrical power systems needed for the pioneering Swansea Bay tidal lagoon and similar marine energy projects around the coast of Britain.

If the government doesn't decide - and quickly - to suck dry the wallets of electricity consumers then these jobs will be lost. All of which is to get the economics of jobs entirely wrong. They are a cost, not a benefit, of doing something.

If we don't build the lagoon then these skilled workers will go and do something else. We will therefore benefit from their output doing that other thing instead of the money sink off the Welsh coast.

Clearly, some of the things that they might do, as is true of any worker and their labour, are worth doing. The definition of that being that they create more value than the cost of having them done. The Swansea Lagoon does not do so. That's why the power from it will be the most expensive in the country. The various cost benefit analyses of the various forms of this idea all show that it has a negative present value. That means that the cost of doing it is greater than the benefits to be received from having done it. Or, as we can also say, doing it makes us poorer.

We simply shouldn't be building it therefore. But this then goes on to the labour employed to build it. As even Marx said, the value of labour which produces no value is nothing, negative even. These aren't, therefore, high value jobs, they are negative value jobs. For their output will make us poorer.

All of which does become clear when we get things the right way around - jobs are a cost of doing something, not a benefit. If we don't want to do the thing in the first place then that's proof that the cost of the jobs to do it isn't worth bearing.