Why are we having this inane conversation? The entire British railway system does not run at a profit, it is massively subsidised by central government. There is an implicit and never properly discussed social contract whereby it is accepted that the capital costs of improving the railway fall almost entirely to central government. The bits of the system that cover their direct costs are those primarily in the south-east where there are no reasonable alternatives and where it is possible to charge the more or less commercial fare for the provision of a service. The suburban services in most of the rest of the country do not cover their direct costs and certainly do not cover their overall costs. Perhaps the ECML and the WCML and the Great Western line turn a notional "profit". But they massively depend on the traffic which is fed to them from other lines.
I and many people on this forum hugely benefit from the fact that most of the system has been left open. First Beeching and then Serpell dreamt of cutting the system back to a profitable core. There isn't one. The economics of transport are close to those of a natural monopoly in which arguments from welfare economics (think Pareto) suggest that you subsidise the system for the benefit of us all.
Look at the rate of return generated globally by airlines in a good year, half a percent or 1%; in a bad year a loss. Then look at the implicit state subsidy: massive cross-subsidy from defence-oriented spending. The aviation system viewed as a system certainly does not generate a proper return on capital employed. Nor do the railways in Britain; I suggest that we all get over it and be glad that government (a.k.a. us!) still pays a large part of the billas an entirely justifiable cross-subsidy.
We are now discovering 60 years after Beeching the enormous and usually insurmountable costs of reopening a closed line. Once closed, a line will almost never be reopened even when there is a very strong case for reopening. Look at how long it has taken to get even the glimmer of a hope that Oxford to Cambridge will be fully reopened. Had that line remained open, I doubt anybody today would be calling for its closure.
There may be some inanities, some basket cases, which suggest the possibility of closure perhaps Newhaven Marine is one of them. But for the rest, let us seek ways to minimise the costs and increase the usage and get the best possible social return on a large social investment. I am utterly delighted that the lines to (for example) the far north have survived as long as they have. Let us have no talk of closure; only talk about how to reduce the costs and how to increase the revenues and how to increase the overall social benefit. And we need to be identifying routes that are crying out for further investment or alternatives or both: think HS2, TransNorth, BML2.
End of sermon!