A question for the staunchly anti-closure people: was it acceptable to close (say) Wootton Bassett station? Doing so saved the cost of having a station at that location, and allowed for better service from London to Bristol and South Wales. But it also removed the rail link for a town of 11,000 people, more than were served by quite a few of the minor branches closed.
I'm not staunchly anti-closures per se, but strongly believe that the '60s closures were badly planned and badly executed. So:
No, it wasn't acceptable. Closing Wootton Bassett was straight-up a mistake.
The cost of a station need not be prohibitive. Gerry Fiennes' work in East Anglia showed that you could feasibly convert market town stations to unstaffed halts (Newmarket is the example he cites) and run Paytrains. BRB could have taken those "basic railway" principles and applied them to a lot more lines and stations.
A few short-distance stoppers (say, Trowbridge-Swindon) and very occasional stops in longer-distance expresses, adapted to meet local traffic patterns, would not have significantly affected the service provision for London-Bristol/Cardiff for many years. A basic railway does not require an all-stops service every half hour.
Those are the "why not close"s. But the "why keep open"s are more compelling.
First, there's the parkway potential. Wootton Bassett (closed 1965) is 2.5mi from the M4 (opened from the 1960s, this section 1971). Bristol Parkway opened in 1972. It is not a massive leap to see that there
could be something there.
But second, there's a really obvious analogue in GWR country, 40 miles to the north-east, which springs to my mind pretty easily because I live there: Charlbury. At one stage it was proposed for closure, but (together with almost all the other Oxfordshire stations on the Cotswold Line) it was reprieved. For a while it received a fairly minimal service, one which didn't particularly get in the way of the faster trains to Worcester and beyond. And now look at it - 300,000+ passengers a year, hourly-or-better IETs to London, a roaring success all round. That's a town with a population of 3,000 and an affluent hinterland: 11,000 and a similar hinterland would do, I suspect, better still.
Keeping Charlbury open, while closing Wootton Bassett, does not make consistent sense. One of those decisions has to have been wrong. With the benefit of hindsight, I think it was clearly the Wootton Bassett decision.
Could that have been foreseen? Who knows. As I've said, it wasn't many years between WB's closure and the Western Region's first Parkway. But the "basic railway" approach rebalances the equation. You no longer have to justify full staffing and a super-frequent service. You justify two concrete platforms, a peak-hours stopper or two, a shopping service in mid-morning where the stock allows, and occasional express calls where there's slack. Perhaps the biggest failing of the Beeching era is that the basic railway was not tried more widely.