Presumably the NDP don't want to touch faith based schools for the same reason the Tories don't want to revisit it...
The NDP is trying to tread a very fine line between keeping their base happy and not blowing a rare chance to win power due to some random controversial platform plank, and I think they're doing a reasonable job of it. Ontario isn't Texas but it's more right wing than people give it credit for. That needs to be taken into account when criticizing platforms.
Why is banning religious schools even an issue? It sounds anti-democratic to me.