F? ilte (Welcome) David,
You are right, there are a number of people out there who are trying to use "Celtic" as a way of excusing cultural appropriation. The irony is, they are usually so ignorant about the living cultures of the Six Celtic Nations that they don't even realize (or care) that none of the cultures they try to use as their cover-stories are dead and for the taking, and that the appropriator is doing violence to additional cultures besides the First Nations ones they know they are stealing from.
In many cases, like the Matthews (with their fake Inipis called by a mis-applied Gaelic name) and Frank MacEowen (with his "Celtic Spirit Wheel", which is just a rip-off of his idea of the "Medicine Wheel") they are very obviously tacking knotwork and tartan on First Nations ways. It's frustrating and upsetting, because many ignorant, if sincere, white people buy it. I like to hope it's because the people buying their crap don't know any better, but in other cases I know they know better, but they just don't care about anything but their desire for some sort of escapist spiritual experience. They might as well just do drugs, as that's the sort of thing they're really looking for. OK, not all of them want escapism, but I'd say a very high number of them do, and they don't care about who they're misrepresenting or ripping off in the process.
The "Celtic Shaman" creep you posted about in the other thread is a real obvious appropriator. In other cases it's been a bit more subtle, and hence more difficult to educate people; such as when someone who's done some good work in the past gets off track (including some, I hate to admit, who I've even worked with and co-authored things with in the past (if never again)) . Even the Matthews initially wrote some good things about Ceremonial Magic and Celtic Christianity, but then they jumped on the Harnerite, Shameon bandwagon. And in the case of someone I used to write with, she decided she has every right to rip off Chanupa and Inipi ceremonies "because the spirits told her to." Thing is, none of these people would be doing these things if they hadn't read Harner and his ilk, so I have to be quite dubious about what the alleged spirits are allegedly telling them. I think it's all in their heads, and most of them wouldn't know a real spirit if it bit them on the ass.
So, we've had people do things like claim a practice is "universal", yet when they write about it or perform it for others, it's just a First Nations ceremony with some misunderstood, mis-applied, and mis-pronounced Gaelic or Welsh grafted onto it. Most of the time, as they actually have had no contact with legitimate, traditional First Nations or Celtic cultures, the ceremony is just a fantasy mishmash of Newage ideas of North American and Celtic cultural/spiritual practices, with no legitimate connection to any of the cultures being stolen from.
Anyway, its a sore subject for me, too, as I'm in the position of recently realizing that one of my colleagues was not what she pretended to be, and it has caused a split in one of my communities. The obvious appropriators, with all their typos and crass claims, are easy to deal with. The articulate ones who do have some genuine learning, and who have done some non-offensive things in the past, are often harder to get people to see the truth about.
Again, F? ilte, agus Sl? inte Mhath (Welcome, and Good Health/Strength/Wholeness),
-Kathryn