normal people should be able to cook with these foods because they probably dont have the same 'digestive sensitivities' that we do. Garlic and onion (as well as spicy foods like chicken wings) only cause minor irritation to healthy intestines but if your intestines are in bad shape it can possibly irritate them badly enough to cause the lips to flare up like what happened with WGB..
try holding a piece of garlic or onion to your skin for 5 minutes I gaurentee it triggers a fairly strong immune system reaction... your intestines are extremely sensitive (much more so than your regular skin), if intestines are damaged in any way and you constantly eat foods which are irritating they will NEVER heal!