Just wanted to point out, plants are obviously not "poison". Humans are omnivore and in the best case scenario, for most people the best diet is a mixture of the 3 main types of macronutrients: fats, proteins and carbohydrates (but not in equal proportions necessarily). It is ideal for most people to eat meat, diary or plants unless there are factors and circumstances than affect this. There are indeed humans who eat only meat, people that eat only plants etc. and neither of these scenarios are ideal for most people. There are also factors that can affect what kind of diet is best for each human such as health level and the amount of energy they consume, the environment in which energy is consumed, for example if you have to sprint at a marathon, meat is not going to help you for a quick boost of energy (something which carbohydrates do) but it is going to help you the most in situations of maintaining saturation and long term conservation of energy.
But indeed refined sugars are indeed "poison" if consumed in large amounts (which most people do) and in fact the "safe" levels of refined sugar that is indicated for consumption is so low that is better and easier to just simply stop eating it completely, except in situations when you really cannot avoid it such as when is added in certain normal foods. Meat may have all the nutrients needed but it may not have them in ideal quantities. For example fibers are a type of carbohydrates the body needs for gut health and other benefits, you might be much better off to eat fibers from fruits or other sources that have it in much higher quantities than meat. As Vivek said above is just a matter of having a balanced diet, and lifestyle. It is also different for each body (due to genetic differences etc.) what combination of fats, proteins and carbohydrates exactly is the most optimal for long term health.