Arguably they're equivalent statements.

>Having Slaves because it's an easier life for the larger population for example?

Yes. Just because you don't like it doesn't mean it couldn't be the "best". By the way, historically, slave-based economies needed the majority of the population to be slaves. It makes sense, since the slaves are consuming their own production and are expending more energy than the non-slaves.

>Try to mathematically proof that ;)

Humans don't grow arbitrarily large or small, nor do they grow arbitrary numbers of limbs, nor have arbitrary numbers of bones. A person chosen at random from anywhere in the world isn't equally likely to hold any opinion from the infinity of opinions they could conceive of. For example, I could confidently say no person has ever simultaneously believed that Google should be subject to more regulation and that the current pharaoh is a living deity.