I have seen many beautiful man-made crystals, and I can respect that people adore them, but for me, I will only accept natural, untreated crystals. Part of my admiration for crystals is how they are real art from mother earth.
No matter how beautiful a crystal is, when I find out it's not natural, I place no value in the product. I know many people will disagree, but it's just how I feel about them. I'm sure my wife wouldn't like it if I bought her a lab-grown diamond, even if it had the same chemical compounds as a natural diamond.
I know I am not alone, many gem dealers in India state that treated or man-made crystals have no metaphysical benefits. For me however, it's not about the metaphysical properties, just the natural beauty. A lab grown/treated specimen might as well be a piece of glass.