The reports of cleaners standing around for hours applying 'anti-dye' to rugs, waiting for the 'excess dye' to come out, are an indictment of the folks who peddle this foolishness. If the guys who sold these chemicals actually washed rugs, and ran successful wash plants, they would't buy this crap either.
It's mostly just "fear" based marketing...."they" blow the potential problems out of proportion, in a multitude of forums and ways, then are standing right there to sell you the "solution". I wonder if most of the buyers of anti-dye and related products have ever washed a rug with dye migration without this stuff. Most of the time color will not set back into the surrounding, lighter colored fibers if proper wash/extraction related procedures are followed.
I've never doubted if this class of chemicals actually works, I'm sure it does, the science makes sense. But for the way my mind works, I'd like to work smarter...not harder (or less efficient, more expensive, etc.) and it seems to me that learning from the true "experts" in this field you find that honing in on a certain set of skills, and practicing those, you can become not only more knowledgeable, efficient, and profitable but truly more confident. The "fear" that a lot of folks have starting out can begin to fade.
With that said, there is a place and a time for use of these chemicals, like Robert stated earlier, mainly with intro level cleaners. Once confidence and skill levels increase these kinds of chemicals will become less and less necessary to produce quality results.
However, it seems that the "fear" mongering continues even with some of these users gaining the skills and confidence necessary to move away from these products. There in lies the problem and the cyclical nature of this type of marketing and thinking, it's designed to keep people just "sick" enough to keep using the stuff. "They" would rather you didn't see the other side, where using these types of chemicals is not common.