[DiogenesKynikos]

Agreed - OP's criticism is way over the top.

This blog post is very much "first principles" for the layperson. It's not the level of "first principles" that a trained physicist would expect (where there would be rigorous derivations involving dielectric functions and the like), but it's great for a layperson who wants to understand why the world looks the way it does.

[godelski]

So then, why use that phrase and not a more accurate one?

[DiogenesKynikos]

Because it's a widely used phrase that everyone understands.

What the "first principles" are for a layperson and a physicist are different, as is the expected level of rigor in the derivations.

[godelski]

  > that everyone understands.

We wouldn't be having this conversation if this were true

[DiogenesKynikos]

No, we're having this argument because of pedantry, not because someone doesn't understand the term "first principles."