I agree and disagree with you all.
<3
Seeing as I'm not on anyones side... lets break this down to its components.
Carnivores all eat the stomach contents of their prey. For he majority of carnivores, this is the first part to be consumed.
The stomach and intestines of prey animals contains essential bacteria along with pre-digested foods... this varies according to the prey being consumed. They may also contain vitamins and minerals lacking in the flesh of the prey. In general, few other organs are consumed, depending on the carnivore.
The vast majority of prey taken is either herbivorous or omnivorous... allowing the carnivore the chance to consume indirectly, the vitamins it needs from greens that it simply does not eat.
So. Clearly this comes down to choice and once again providing a balance according to how your animal has evolved.
Monitors are primarily scavengers
I see zero reason a monitor could not be fed chicken necks on rotation with other meats, if the meals are planned to contain an over all balance. Being opportunistic, their diet would be all over the place, balance would be attained over a period of time, rather than with every meal consumed.
Snakes have evolved to consume whole prey... they are ambush predators. They can conserve their energy and have a low metabolic rate. This comes with both plus and minus. The snakes have however evolved to cope.
The only clear benefit I see to feeding whole foods is that it would have a natural digestion process and length. If feeding parts, you would need to be careful with the rate of digestion and I guess primarily the fat content. As far as what affects a faster digestion process would have, I have no idea. Perhaps it would allow the snake to increase its metabolic rate. And perhaps this would be of benefit in the breeding season. I certainly see the benefit in using pieces to put condition on a snake.
Here's another thought... in the wild the stomach contents of prey animals is highly beneficial... because it is normally consisting of a predigested food substance carnivores themselves do not consume.
So with commercially available animals, who are long fed cheap food to sustain and grow them (normally in the form of commercial pellets) what is the point of the stomach contents? Do we know that the rodents being fed have a natural gut bacterial balance? Are their stomach contents at the time of death rich in vitamins consumed in the foods of herbivorous or omnivorous animals? If this isnt the case then the argument for feeding whole again becomes moot.
You can't know your animal is getting its essential balance.
Though... if you are feeding a primarily reptile eating animal on primarily mammal prey... then I think you might have less basis to criticize others feeding choices than you think