Ballachulish branch.
 

Now most of the beeching cuts had good reasons behind (supposedly), but in a recent book (lost lines od scotland I think or something like that), apparently freight traffic on this line was prospering at the time of closure, and had over 25000 tonnes of freight a year (I can't remember the exact figure, but it was higher than that I'm sure), and that sounds like enough to keep it open.

Why they closed it then is a mystery. Passenger traffic was pitiful though. Its a shame about this brnach line as it had stunning scenery.

The branch infrastructure was quite expensive to look after, particularly Connel Bridge which was also a noted bottleneck as the railway shared the bridge with a single track road, but both could not use the bridge at the same time.
The alternative for road transport was a massive detour around Loch Etive, so it was really a no brainer that once passenger traffic stopped then the railway would have to close so as to allow road traffic exclusive use of the bridge to cope with the ever increasing road traffic.