I'm a bit of a purist, I think. I trust (?) evolution, in some sense, and don't think that we should be meddling with it on a broad scale. If we're really giving such thoughts the time of day...history has shown time and again that humans can't possibly understand all of the complex and nuanced ecological connections on our planet. Not-fully-informed meddling with ecologies- such as non-native species management - has already done quite a bit of harm. Furthermore, without carnivores, there are many obvious ways that our ecosystems would be completely thrown out of balance (i.e., imagine what happens when the planet is overrun by herbivores who are eating all of the vegetation).