My point was that Mab is cruel for a reason, not evil for evil's sake. Taking fae creatures' children to fight against the Outsiders isn't nice, but it is necessary. Within their context, what both Mab does and the Spartans did served purposes; Mab is preserving Reality itself. Sparta was preserving itself. Both employed brutal efficiency.
The context of the point wasn't to say that Spartans were nice or excuse what they did, merely to point out that the horrible stuff they did throughout their (brief) history made sense in the Iron Age, and comparison to modern morality is like comparing developing nations run by dictators to Norway.
And the rest of the Grecian city-states sure were glad to have Sparta around when the Persians came a-knockin'. Just like Reality is glad that Mab's there.