Why is cannibalism bad?

On average people will invoke something like the holiness of the human or a decree of a divine nature. But Spinoza would say that in such cases science has to supply the answer.

We now know cannibalism causes the human version of mad cow disease. As with incest, it’s the damage, the obstruction of the development of optimal human potential, that makes cannibalism bad. 

These types of questions provoke a battle between reasonable, empirical arguments and those of other origins. Moreover, research and thought also evoke insecurity and the realization of incompleteness; many people find this threatening. 

In Spinoza’s case, this led to some regarding him, as they did Machiavelli, as a diabolic thinker.