Why Carnivores Should NOT be fed Other Carnivores
Carnivores probably have a higher incidence of parasites that can be shared among other carnivores, but the biggest hazard comes from biomagnifications.
Biomagnifications has its roots in the energy loss between tropic levels in the food chain. Plants are at the very bottom - they get their energy from the sun, which, for the most part, is inexhaustible. The next level up is consumers, like cows, rabbits, and so on. They consume the plants. The plants use energy for their own, for growth and maintenance... which means that there is an energy loss between the sun and the consumers. The next level of consumers (the carnivores) must eat even more herbivores, because the herbivores use energy from plants to grow, move around, and reproduce... which is another chunk of energy lost.
This means that, as you go up, each level of the food chain must eat an increasing amount of mass from the level below it. Rabbits can survive on a kilogram of grass, while a fox would need 2 kilograms of rabbit, and a wolf would need 3 kilograms of fox, and so on and so forth (we just pulled the numbers out of thin air to demonstrate the concept - they're not accurate).
The problem is, organisms acquire heavy metals, radioactive compounds, and other toxins from the environment. Some of these are human-made, while many occur naturally. They mainly enter the food chain through plants (which absorb water and nutrients from the soil, along with the toxins). The plants get eaten by herbivores, which get eaten by carnivores and so on. Since each level of the food chain must eat an increasing mass of the level below it, the concentration of these toxins *increase* as you go up.
As a result, carnivores would have a higher level of heavy metals, radioactive isotopes, and carcinogenic compounds than the herbivores would have. These can't be destroyed or removed by cooking and this is why carnivores shouldn't eat fellow carnivores.
Simple right? However, there seems to be a little confusion over whether you can feed omnivores/insectivores to your carnivores, these eat meat also right?! Whilst this is true, meat isn’t their only food source. Chickens, for example, will eat insects and sometimes each other, but also eat vegetables, grains and other ‘primary’ energy sources. Pigs will eat meat also, but also consume vegetables, plants, etc., again these are ‘primary’ energy sources. Biomagnification isn’t an issue with these foods, because plainly and simply meat isn’t their only food source.
It is perfectly safe to feed omnivores and insectivores to your carnivore.