Raw foodism centres around the incorrect belief that uncooked food is intrinsically healthier than cooked food. Firstly, there is no evidence to suggest humans were healthier when we only ate raw food. Experts believe that cooking likely contributed to human brain expansion, as it reduced the need for large teeth and jaw muscles, thereby allowing larger brain evolution.
On top of that, raw food does contain ‘live’ enzymes, yes. And cooking does denature these enzymes, thereby rendering them non-functional when heated above around 40°C. You know what else denatures enzymes? Your digestive system, duh. Your stomach sits at a comfortable pH of around 2–3 thanks to the production of gastric acids. That’s highly acidic, as enzymes such as proteases which break down proteins function optimally in this kind of environment. Your body can’t use plant enzymes; they get broken down in your stomach just like any other protein would, and your body uses the resulting amino acids as building blocks to make other proteins. Your body doesn’t ‘recruit’ plant enzymes for its own use. Essentially, plants use plant enzymes, humans use human enzymes. End of.
Finally, cooking food may ‘kill’ (if you want to use such dramatic language) the enzymes in food, but that doesn’t render the food ‘toxic’ or a nutritional wasteland. Cooking food kills bacteria and parasites that could harm you. In some cases, cooking food can break down some vitamins, yes, but in other cases it makes them more bioavailable (i.e. easier for your body to use). So, it’s not clear-cut and it really depends on the food.