The sad truth is most people are going to get something like a ball python from a pet store, not a reputable breeder. So you don't really know what the snake has been fed, and how it has been cared for, meaning there's not a really good way to know how big it will get, or whether it will have problems with picky eating and so forth.
Unless you can get them from a breeder, I don't think people should keep snakes, anyway. They're not really pet animals. I have heard lizards are a little more responsive, but I've never seen a friendly snake. I've seen docile snakes, and non-aggressive snakes, but none I'd really term friendly. I don't think they really have that capacity. Not maligning them -- it's just not part of their makeup.
I don't care for snakes and wouldn't ever have one, but neither do I think they should be raised en masse and then poorly cared for. Snake mills are just as inhumane as puppy mills.