If you cannot honor the source of that which you make use or use something of significance to a culture other than your own to mock or repurpose without asking permission or at least showing respect then, yes it's offensive.

So, let me get this straight. By that reasoning, if Wynton Marsalis uses a trumpet to play jazz without thanking the white Europeans who invented the instrument, that's okay, but if he uses it to play polka music, and rolls his eyes mockingly while doing it, then that use of the trumpet is cultural appropriation?

I have another idea. Let W.M. do whatever the f#@k he wants with it.

examples range from the frivolous (people complaining about the corn rows hair style as the "Bo Derek look") to the genuinely racist (Col Parker looking for a "white nigger" to make a mint off of and using Elvis Pressley to make his fortune while never remunerating or acknowledging the black artists they got the material from).

It's a difficult topic to nail down. But the rules of thumb I use are (1) is it demeaning or dismissive of cultural origins? and (2) is it tied to exploitation or oppression of other cultural groups?

American artists who draw from the fullness of American culture will inevitably draw influences from artists of diverse backgrounds. Honoring the source material and being non-exclusionary is how this cultural sharing can happen without being exploitive. A professor I know uses the Vanilla Ice - Eminem comparison.

I think the concept is poorly understood and often applied incorrectly.

Quite honestly one has to also understand and acknowledge that it has been going on for thousands of years.

In the current environment, I think it is a legitimate gripe that the adoption of certain practices for in essence "inappropriate" purposes is what is being referenced. Basically, if you are adopting a practice as it is intended to be, that's acceptable. If you are basically mimicking a practice, especially out of context, you're probably in trouble.

If this is your understanding of what cultural appropriation is, I encourage you to read more about it.

To "cultural appropriation," which is often used as an accusation: "you're stealing my stuff!"
When people of various cultures inhabit the same geographic space, they will impact and change each other through the processes of their interactions.
Being asked and agreeing to wear a yarmulke is different from coming to a Seder already wearing a yarmulke without having been asked.

But I'm willing to change my mind if someone can explain to me how it makes sense.

Specifically, I'd need an explanation of why it's wrong to appropriate X's culture when it's OK that X wears blue jeans, has an iPhone in his/her pocket, uses PCs and the internet, watches Hollywood movies and T.V. shows, etc., etc.

That members of only one culture created any of those things?

If I find something I'm doing is offensive to some group, I stop. Of course, a fair proportion have to actually care, but I don't get to decide if they should be offended, they do.

Of course, if the offense is just taken by the overly sensitive sorts who always rush to be upset, they'll have to lump it. But even then I'd try not to upset them if we met. Bless their prickly, unbalanced little hearts.

That said, I don't see anyone of note or substance arguing it should stop, or reduce its velocity.

Everything else in your post can be addressed by simply opening our eyes and ears as individuals as ask "am I myself being respectful?"

Granted, those too-clever-for-their-own-good can easily deconstruct the question "am I being respectful" to such a degree as to rationalize any behavior in themselves, but that's simply because they're not asking themselves the question with sincerity, but rather with a defensive agenda.

I reject the notion that Paul Simon, for example, was being insensitive and disrespectful for writing and performing Graceland or Rhythm of the Saints. I say lay off, and be proud that someone else wants to participate in something you created.

I find the term cultural appropriation a bit annoying