Many people use dish soap. I checked with DuPont Auto Finishes who recommended against this. I'm sure you'll read about people who have been using dish soap for years, but they must know more than a paint engineer at DuPont.
The R&D department at Dupont performs tests to see the results of different products on their finishes. Then they make "recommendations" as to what they believe is best. Why did they make the recommendation? Does it harm the finish? Does it leave streaks? Is it not effective?
By using dish soap on their vehicles finish and witnessing the outcome, those that like dish soap are performing an unofficial test. If they perceive that there is harm, I would like to think they would stop. Do they know more than a paint engineer at Dupont about paint? Probably not. But they know what they like.
Over the years, I have used whatever surfactant comes to hand, and all I know is that at the end of the day, my car is clean. After all, its just soap.