My understanding is that balloon mollies, at any rate, have a higher rate of health issues and decreased lifespan as a result, because of the spinal deformity. That ranks as cruelty and "hurting the fish" in my book, even if it doesn't affect every specimen, and isn't constantly observable.
I don't agree with it because most times the fish end up with life shortening deformities. And I usually don't find them aesthetically pleasing, even though I do feel pitty for them. They couldn't help it.
What about the "Deformed" Goldfishes?? The No Doral fin, the 2 tails, the Orandas, the Lion heads??