“plants are poison—they don’t want to be eaten, and have, as a result, evolved defensive chemicals designed to disrupt your digestion”
As if animals do want to be eaten. I’d argue that animals don’t want to be eaten even more than plants.
It's far more difficult for a prey animal to have its muscles/fat/organs suffused with chemicals that will kill/injure its likely predators, especially if its predators have similar metabolic pathways as itself -- it'd be at risk of poisoning itself if the poison broke free!
Animals certainly fight back against being eaten (running away, fighting, etc) but once they're dead their meat (barring like, snake venom glands or pufferfish or other poison/venom-suffused sea creatures) won't fight back.
Obviously "plants are poison" is phrased for shock value and there are traditions and safe handling practices (like "cooking", or "not eating green potatoes" https://en.wikipedia.org/wiki/Solanine) for plants that remove, denature, or prevent the formation of defensive chemicals.
So the idea that it’s inherently better and healthier to eat animals because “plants are poison” is not only on its face a bad idea, but it’s also a bad idea upon closer inspection.
(As an aside, I highly recommend Bill Bryson's "At Home," which discusses these topics and many more related to how we came to live the lives we do -- it's a great companion to A Short History of Nearly Everything.)
But the plants are poison idea ignores a very important point - that we eat the parts of plants that have evolved to be eaten, by us and other animals.
For the most part we eat only the seeds and fruit, and we help spread them in an almost symbiotic relationship.