I've had the opportunity to read Letter 52. The first thing that struck me was the tone of the letter. It very much strikes me that Tolkien was angry. Angry that governments conduct these awful wars, and now his 18-year old son has been thrust into it, presumably against his will.
As others have noted, Tolkien's anti-mechanism sentiment comes through strongly:
There is only one bright spot and that is the growing habit of disgruntled men of dynamiting factories and power-stations; I hope that, encouraged now as 'patriotism', may remain a habit! But it won't do any good, if it is not universal.
One supposes that Tolkien wishes to go back to the days of horse and buggy and reading at night by candlelight. Perhaps he would have been happy if we lived like the Amish. What do you suppose that Tolkien found so objectionable to technology? (Besides the marring of the natural environment, of course.) Did he feel that it dehumanized us?
That makes me think of a silly song that Alan Sherman wrote to the tune of 'Imagination' called
Automation. In part it goes:
I thought Automation was keen
til you were replaced by a 10-ton machine.
It was that computer that tore us apart, dear,
Automation broke my heart.
There's an RCA 503
standing next to me dear where you used to be.
Doesn't have your smile, doesn't have your shape,
just a bunch of punch cards and light bulbs and tape, dear.
You're a girl who's soft, warm, and sweet
But you're only human and that's obsolete.
I'm not very fond of that 503, dear,
Automation is not for me.
Sure, there are a lot of drawbacks to mechanization, but there are a lot of positives, too. For instance, making a lot of goods available to people who never would have been able to afford them in 'the good ol' days'.
I find the reference to "whiskered men with bombs" most curious. In our own time we had one such person who, as it so happens, was also very much against technology: Ted Kaczynski, aka 'The Unabomber'.