You don't know your biology and chemistry very well, do you? Turning your nose up at something just to break "the rules" is very irresponsible, especially when there actually are documented cases of this going wrong and very valid medical reasons for not doing so.
Contrary to belief, stomach acids don't heat anything; they break substances apart, which means the internal temperature of a partially frozen rat does not change during the process of digestion and the frozen bits inside would thaw the same as if they were still on the outside.
Edit; Looked into it further after posting. It actually has more to do with the fact that at low enough temperatures a snake can't digest properly. Feeding them food that is still frozen in the center is effectively dropping an ice cube into the stomach of an animal that needs to use its environment to thermoregulate and therefore halting its digestive processes.






