The Predation Defense

Lately I've been torturing my family with the question: what would the world be like if all animals were herbivores?  I'm pretty sure the answer is: not as good.  Evolving to hunt makes a species develop all sorts of perceptual and cognitive strengths, and likewise, evolving as another species' prey.  I can't see how a world filled with herbivores, and only herbivores, could have minds as