Plants contain natural toxins that have to be cooked or prepared out of them
True, and it is not specific to vegans. Everyone eats beans, potatoes and grains, and the usual preparation (soaking, boiling, not eating green potatoes) deals with it. Meat also has to be handled and cooked properly, and it causes a large share of food poisoning.
Plants are not passive. Many defend themselves chemically: raw kidney beans, green potatoes and unprocessed cassava can make people genuinely ill. A diet that leans heavily on plants leans heavily on preparation knowledge that not everyone has, and advocates who present plant foods as simply wholesome are glossing over a real hazard that people should be warned about.
Yes, some plants contain defensive compounds that need dealing with before you eat them. Raw kidney beans contain a lectin that causes sharp stomach illness, and boiling them properly destroys it. Green or sprouting potatoes build up solanine. Cassava has to be processed to remove cyanogenic compounds. None of this is in dispute.
What it shows is that food needs preparing, which is true of every diet. These are not vegan foods. Omnivores eat beans, potatoes, rice and cassava too, and the knowledge needed is basic: soak and boil dried beans, or buy them tinned and already cooked; throw out green potatoes. It is mostly passed down in kitchens, and in cuisines built on pulses it has been for centuries.
Meat carries its own preparation risks, and they are not smaller. Salmonella, campylobacter and E. coli are commonly present on raw meat and poultry when it is bought. It has to be stored cold, kept away from other food, and cooked through, and cross-contamination on boards and counters is a common route to illness. Ground beef and poultry account for a large share of recorded outbreaks. A diet that includes meat swaps one set of preparation rules for a larger one, not none.
The better test is outcomes. Where legume intake has been studied over the long term, higher intake is associated with lower cardiovascular risk and lower all-cause mortality, and replacing meat with legumes is associated with lower coronary heart disease risk. That is the result after the occasional preparation mistake is counted in. Compounds like phytates and residual lectins in cooked food are often called antinutrients, but at normal intakes they have not been shown to cause harm.
So the point is fair as kitchen advice and worth teaching. It is not a reason a plant-based diet is riskier than the alternative.