I'm sure exactly what you described was done plenty of times in ww1 and similar around that era, and seen as perfectly moral and rational.

The materials and labor for a single plane are far lower.

There is zero reliable evidence that these things impact how the instrument sounds or plays, or that guitars age in any appreciable way (maybe acoustics, but certainly not electrics). Manufacturers are cranking out amazing instruments with remarkable consistency, we're truly in a golden age where even low tier instruments are likely to be every bit as good as what the 'greats' played on, which were after all just off the shelf guitars in their time.

Lets start with the assumption that it is possible to make a meaningful impact on climate change by significantly reducing our consumption, this requires significant sacrifices to an individuals lifestyle.

I'm talking big pictured stuff like not eating meat, no more international travel, no personal vehicles, less spend on medicine reducing life expectancy, limits on number of children.

Lets say we have credible evidence that if these things are done the situation will improve.

Now whether you take the perspective of being an individual, member of a community or even a country, why would you make those sacrifices if you have no guarantee that everyone else will. It's a big price to pay to 'set an example'.