How did Islam destroy the classical world?

[abaris]

True, but what of all that Muslim military activity in Europe, and the undisputed enslavement of a million Europeans?

I guess, you're speaking about the Osman empire, cause otherwise I wouldn't know of any expansive muslim power after the early Middle Ages when they conquered the Iberian Peninsula. Read up on the Kalifats there and the administration of the Osman empire before we take this any further. Especially on the role christians as well as jews played there. They weren't slaves and could rise to the highest administrative ranks. They only were taxed for excercising their religion, not prevented from doing so.

Ghenghis Khan told people straight up he was there to kill them and take their stuff.

Obviously your knowledge of the Mongolian empire and it's administration is confined to children's books and common prejudices. Just as with the medieval muslim world.