A person posting on a military aviation newsgroup provided this link:
Weldon letter to FAA
Assuming it is for real, which seems likely to me:
His criticism is so comprehensive, and so over-the-top that is has far less
credibility for me than would a more focused objection to specific design
problems or management actions.
Essentially he demands that no new structural material differ in any way from his beloved aluminum that could ever have any adverse effect under any subset of use conditions. He also takes a commitment to overall safety improvement, and translates it to a requirement for no adverse safety impact in any circumstance, no matter how implausible.
That not only rules out composites, but pretty much anything else. If one considered titanium in a similar mood, I'm pretty sure you could find some killer objections. It is hard to machine, for one thing, so with equal production skill, more likely to have some sorts of flaws.
I'm not saying none of his concerns have any validity. I think maintaining composites appropriately for cases of "hangar rash" and such may take some real field experience and learning before cost and safety get balanced properly, just to pick one.
I am not a pilot. I am a retired engineer, with some experience in arguing unpopular views in a large organization.