Nietzsche saw the treatment of the weak (e.g., exclusion or punishment) not as cruelty but as a necessary expression of health and order.

This was closer to the moral structure of Rome which is analogous to the moral structure of groups like ISIS who used similar means in their punishment of those who were conquered (and therefore weak).

These ideas appeal to authoritarians who believe their strength needs to be respected and those in their way can just die.