Well, there was a big discussion on this here and also on a FB page with some authorities in reptile lighting and heating involved. Bottom line was that a gradient is required for the long term health of the animal regardless if some people have "success" not doing it. For some people keeping snakes successfully equal that they stay alive, feed, and breed. It's impossible to tell whether a reptile kept at a constant temp is feeling good, or it just accepts the fact as it's out of his/her control.. What we can go by is what they do in nature.
Reptiles can be very hardy and survive a lot of punishment. So unless someone develops a method to communicate with them and/or does scientific research on the long term effects of being deprived of thermoregulation, I'm not buying that it is in any way or form better for the animal.
similar logic is applied by many BP keepers that it is OK to keep them stored away in a tub in a dark shelf because "They live in termite mounts in nature". This comes from a period in the year when the snakes do in fact retreat in termite mounts or other holes because it's too damn hot outside and are collected by people for the pet trade. This translated into the current keeping method.
In fact male BP live in trees and hunt mainly birds, they aren't really found in holes in the ground. Females on the other hand tend to be more terrestrial and live around scrubs and bushes. Give you BP some height in a vivarium with large trunks of wood and you'll find he/she will use it very often.
Another often missed aspect is lighting. Reptiles have 4 cones in their eyes and can see UVa light. Not providing proper lighting to your reptile, f.e. skipping UV, basically makes your snake experience the world in a weird hue for it's entire live. Imagine your whole world would be without blue... now you'll think maybe, big deal so the sky is gray, but having no blue affects all the others colors too... here's 2 pictures where I took blue out of one;
Original
And no blue
So it's kind of a big deal for someone deprived of this color.