Quoting from some of the lines in the cartoon
There are no such things as a good drug and a bad drug. There's this chemical that's neither good or bad, it just exist out there. We either create it or it exist in nature. And then it's the relationship that human have with the substance that is the issue.
Curing zombies can turn them back into humans, but we do it in the midst of zombie/human combat, so the zombies that turn back into humans are quickly eaten by other zombies. The longer they stay zombies, the longer they live? A very ironic situation that I could have stayed.