What kills me is that the people who are complaining about this being cruel are probably the same people who complain about venomoids.
"Taking the venom glands is cruel, not what nature intended." Well in the case of kingsnakes, this is what nature intended. If our responsibility as herpers is to replicate nature as much as possible then, if this is an affordable alternative in your area, then you are providing for your animal as best you can.
Nature didn't intend for snakes to be kept in captivity so there no one can say that any one approach is 100% right.
We all deprive our animals of some things within their natural requirements (ie; freedom of movement, natural changes in seasons, and natural diets) while giving them others (ie; security from predators and disease).
We have no way of knowing for sure if there isn't some biological reason why kingsnake need to eat other snakes in the wild. If you don't want to watch reptiles doing what comes naturally to them then go find yourself a gardening site or something.