BR was losing money in barrowloads at the time Beeching took over. If the network as a whole was using money it's ludicrous to suggest branch lines with a couple of dozen passengers a day were not making a loss - or even particularly useful even if you ignored the financial aspect - in some cases a free taxi service would have served the public just as well.
You conveniently forget that
after the 'Doctor's Surgery' the losses continued to rise. The flawed analogy of the time was that the railway system was like a tree with the trunk feeding the branches when, in truth, it worked the other way with the exception of some seaside lines. Some lines had outlived their purpose and pruning had been going on for many years but the 'Beeching Plan' was fundamentally flawed because it considered branch lines in isolation rather than as part of a network. Do you really believe that all the closures were of 'branch lines with a couple of dozen passengers a day?'
The valley services into Newport carried thousands of passsengers but were chopped for operating convenience and to save money on the MAS Scheme then in progress. The footfall at Newport fell markedly after these closures as passengers from the valleys, travelling to Bristol and London etc., deserted the railway completely. The Aberdare, Aber Valley (Senghenydd) and Maesteg lines went because they operated in isolation when they should have run through to Cardiff. The Vale of Glamorgan line was in a similar position with very little through working. It should also be noted that no attempt at cost saving was made and all of those lines had fully staffed stations until the day that they closed. On the other hand, all of the services that ran through to Cardiff survived. None of the lines, that I have listed, fell remotely into your category as candidates for closure but were the victims of a flawed and arbitary ideology.
It is interesting to note that, with the exception of the Aber Valley (now beyond reclamation), all of those lines have been successfully re-opened and all, without exception, run through to Cardiff. Ebbw Vale is an interesting case because it formerly served Newport and some concerns were raised that it might not appeal to the good people of the Western Valley who had, historically, been drawn to Newport rather than Cardiff. In the event, the five year target after re-opening was met within three months.
I know this area very well and, as a railwayman, worked all over it. Many unforgiveable things were done by the Beeching / Marples axis to appease the road lobby and subsequently by Wilson's government which was in the pocket of the T&GWU. I don't know how old you are but I can assure that 'political spin' was just as prevalent in the Sixties and Seventies as it is today.
Remember it was Marples who stated that it would be cheaper to buy us all motor scooters than retain rail services. Yes, a catchy kind of slogan but it makes no mention of those unable to drive, for a variety of reasons, mothers with infants and children, the elderly, the disabled ranging from severely disabled to unsighted and everything in between. How do you get a push chair on a scooter?
Some lines, as I have stated, had outlived their purpose but, in many cases, the baby was thrown out with the bath water.