Herbivores do not need to cook their food first, but we humans have done that for many tens of thousands of years. Proof of that is the reduced size of our teeth and jaws.
You can live on mainly animal flesh, but that means you have to eat the organs too, not just the meat. Organs like for instance the liver and kidneys contain all the vitamins and nutrients we need, and that's how the Inuit have lived and survived for thousands of years.
Plants and trees are living beings, they sense, and they can do a lot more (see other thread in the Natural forum here). That they don't have a nervous system doesn't automatically mean that we can tell how they "experience" life; we have not the slightest clue.
Btw, here's a video of a deer turning carnivore (I have seen cows do the same):
There deer is doing that purely for survival.
Which adds to my point.
We don't need meat, we are only capable of it for survival reasons. Gorging on meat like we do is not survival.