Veggie burgers have all kinds of hard-to-pronounce ingredients, from protein concentrates to binders, whereas meat has only one ingredient: meat. So between the processed foods and all the ingredients, veganism is unhealthy.
Veganism supposedly limits the number of foods you can eat, and is unnecessarily restrictive. But this argument is literally saying eating fewer foods is better. So which is it?
These claims alternate between "food with a multitude of ingredients", or "difficult-to-pronounce ingredients". Neither of these have any scientific basis.
This is just bad health advice based on some idealized version of how cavemen lived (and therefore "that's how we're supposed to live") or some other fictional idealization that carnists have. If you disagree, see if you can count up all the ingredients in your Lipitor that you're taking after eating how evolution "taught you to"?
No one is forcing you to eat a particular veggie burger or other food. If you don't want to eat something just don't eat it. There are plenty of alternatives such as beans, soybeans, lentils, etc. that can be great sources of protein and have only a single ingredient.
Not only do many meat products explicitly contain flavoring ingredients (Examples 1 or 2) which is no different from all these "extra ingredients" these veggie burgers have (oh no, not vinegar, cherry color, and paprika!), but they have straight-up preservatives. Do you actually expect me to believe that at every grillout you're fishing packages out of the trash and counting up the ingredients on the carton and, more importantly, if the veggie burgers had fewer ingredients you'd give one a shot? Probably not. Would you also refuse to take vitamins because then you're adding to the number of ingredients you're eating in a day? Also, plenty of carnist foods have tons of ingredients. Are you going to go on equally about those midwesterners and their ranch dressing?
Most "single-ingredient" or "100%" meat is a lie, and also includes things not in an ingredients list like animal feces in every piece of ground beef or pus in milk? Also, are we including the antibiotics and hormones the animals are stuffed with? So, this idea that carnist foods are somehow pure and vegan food is full of chemicals is an oversimplification that just doesn't map to reality.
Let's assume that all of the above is incorrect. Would it ethically justify slitting an animal's throat and eating its (fecal-contaminated) meat because you don't know what some specific chemical is, you don't want to eat it, and it's in everything vegan (including apples but not in a narrow subset of those meat products)?