Many Buddhist societies are amongst the worst slave states know to history (the Tibet from this article, but also Burma and oh-so-beloved Thailand).
And this is not despite Buddhism but because of it. In all societies where it is dominant misfortunes such as being born poor (or worse) are seen as being justified somehow, leading to astonishingly callous mistreatment of the poor and unlucky - think the wholesale enslavement and transport of complete populations such as in Thailand not too long ago and in present day Burma.
Zen Buddhism, too, is a spectacularly nasty piece of work. It originally existed in two variants: one for the peasants, which taught them to accept their miserable lot, and one for the warrior class which taught it that life is fleeting and death inevitable (it is this variant of Buddhism that was used to indoctrinate Kamikaze pilots in WW2)
So why we in the west should think that this is an especially enlightened religion is beyond me. If you must do religion, why not Christianity or Islam? At least these two make a point of encouraging charity and kindness towards others.