I don't see the point in all this historical revisionism. They did what they did and we are where we are.
Whatever their motivation, a particular group of elected politicians, managers and maybe other actors behind the scenes decided (not conspired) to reshape the railways as they did over half a century ago. The architects knew they had to act very quickly as public resistance would grow and eventually bring the process to a stand, which it did, hence the large volume of near simultaneous closures. Maybe in modern eyes they went a little too far, too fast, maybe they didn't go far enough, maybe they didn't do enough to protect some of the more valuable alignments, but it all has to be seen through the prism of broader attitudes toward old 'Victorian Industries' as the railways were undoubtedly seen in the white heat of the post war technological revolution. While some may like to imagine a dastardly plot, the business community and thus the Tory party have by and large always recognised the importance of railways in their core applications, hence the reshaping report also contained many positive proposals for modernisation of what would be left. I have an official Conservative pamphlet from the period which sets out a strong argument that roads cannot be expected to meet all the heaviest freight, commuter and intercity traffic demands for various reasons so railways must continue to be supported for the sake of the economy. Governments of all colours have never given the railways an easy time, but there has not been a realistic existential threat at any time. The bonkers Serpell report emerged from a period of swivel-eyed lunacy in the DoT that by no means represented the broad view of business or the party. Whatever her personal position, Thatcher knew wide-spread closures at that time would have been political poison, and never followed up on Serpell, thank goodness, but the deep cuts to railway capital spending of the time were very challenging indeed.
Rather than continue to argue about the past, I think we all need to maintain vigilance, particularly at this difficult time, of shadowy influences who may wish to damage the industry or limit its development unreasonably in the future. The Conservative party, if it survives Brexit, might swing in alternative directions as to its positions on rail and public transport generally, under whatever new geopolitical interests the nation becomes aligned to, and of course in response to attitudes and behaviour of the public.
As to the past, "The past is a foreign country; they do things differently there".
Those who forget the past are doomed to repeat it.