Quibbling I know, but I wouldn't call it 'stupidity'. Beeching knew what he was doing and he enjoyed doing it. It was for the benefit of Marples and himself, in order to support the motoring industry.
I reckon thats one of these myths that develop and get spread by people who werent there at the time and havent looked at the facts.
Fact 1: The railways had been facing problems from road vehicles ever since something better than the horse was invented. Local steam-hauled services in cities suffered competition from electric trams. After the First World War competition from motor buses and lorries increased. There was a period during and after the Second World War when that increase in competition was slowed down, by fuel rationing, restrictions on the manufacture of motor vehicles and their high prices, but during the 1950s fuel restrictions were lifted and more and more cars and lorries became available. So the competition facing the rail industry intensified.
Fact 2: Rail closures were taking place throughout the twentieth century before Beeching. Certainly, Beeching proposed closures on a larger scale than had happened previously, but why? Because the railways were losing money and the losses were having to be met by the government from taxation, and it wasnt a situation that could just be left to drift. The solution adopted at the time may not have been ideal, we can now see, but there was undeniably a problem.
Fact 3: There was a public demand for more and better roads, not just around the time of Beeching but for decades before that. The Ministry of Transport was planning and building new roads to accommodate the growing amounts of traffic in the 1920s and 1930s examples are the East Lancs Road, the Southend Arterial Road, the North Circular Road. The Institution of Highways Engineers and the County Surveyors Society both produced plans for a motorway network during the 1930s.
Fact 4: As road traffic began to increase during the 1950s there was a growing public demand for a revival and expansion of the road-building programme. We knew that in Germany they had Autobahnen, autoroutes in France and autostrada in Italy. We didnt. Some locations became notorious for traffic jams. Staines was an example, where the abutments of the bridge over the Thames that was to be part of the new by-pass had been built before World War 2 started. I remember travelling on holiday from Waterloo to Sidmouth in 1957 and seeing the queue of cars waiting to get through Honiton. The opening of the first British motorway, the Preston by-pass, in December 1958 was really exciting, and so was travelling by train between London and Manchester in 1959 and seeing the new M1 being built. People wanted cars, and they wanted new and better roads. These things werent forced on them by the motor industry or the road-building industry or Marples or Beeching.
As always happens, things went too far, and a few lines closed by Beeching should probably have been retained or so we can see today with the benefit of hindsight and in the light of the way things actually are now, which not many would have foreseen over fifty years ago. If you disagree with that just tell us how things are going to be 2067. But in the context of the situation in the early 1960s I think Beeching was largely right, regrettable though it may seem in many respects, and blaming individuals or vested interests just confuses the facts.
(I suspect we may be going to need a new thread about this!)