I can understand those on the side of concluding that Kurt is altering cards, but in reality the "spray" (his other product, the polish - is not for vintage cards) is quick evaporating, and doesn't leave anything detectable on the cards. It just doesn't.
I bought some last year just out of morbid curiosity; not because I was interested in starting a card doctoring business. The spray is described as a "lubricant" by Kurt, and he claims it's all natural. Beyond that of course, he won't say what it is. It's not water, but it also doesn't smell overly chemical. I had moderate success with removing wrinkles (on lower grade vintage common cards in my PC), and more with things like making crunched corners sharp again - and in the end decided that while novel and certainly interesting, a future in using Kurt's products - even if only on my own cards - wasn't for me.
Just my two cents - but Kurt's methods are a sideshow right now, and very much a moot point when you have the top grading companies that cannot detect real alteration - trimming and other more heinous type things in many cases on expensive vintage cards. If the Gary Mosers of the world can get much worse stuff by PSA, then going after someone like Kurt - yes even if you consider it alteration - is going to be a huge waste of time. Another of his recommended tricks which involves putting a card in a humidor really does only use water - and under the right conditions - I would imagine a dent or wrinkle could also be removed from a card with humidity by accident in an attic or something. I don't see how anyone could claim that is alteration - although it's yet to be seen on a lot of those I think if the problem would somehow later "come back." But hey, some 1974 Kellogg's cards in PSA 10 slabs get exposed to temperature and humidity and wind up cracking later in the slab. They're still PSA 10's, right?
This debate will go on, but I would agree that current sentiment in the hobby may see things like some forms of out-of-the-closet restoration become acceptable. Again, I totally agree with the right of those who think it's wrong to hold their own opinions. As with many other things however, sometimes you can't do anything about it.