Some one asked me this question and I said all . All plants have some level of secondary metabolites which are at a very low level of toxicity . Some plants have these substances at sub-optimal and some have at super-optimal level. All substances are utilized in our body at micro-nutrient level and if they exceed that level they become toxic.If one over eats its toxic to body. It depends on a genetic make up a person, his immune system, metabolism and response to external or internal stimulus to get a situation which is not normal in metabolic process. Plants if taken properly in proper amounts in proper manner are good for health but they also provide lots of substances that work against pathogens. If taken in large amounts they can act on our body also. But if taken in proper dosages they are good for health. Why do plants synthesize those toxic substances ? Its for their own defence mechanism against pathogens or to ward off abiotic stress or biotic stress. However all plants do not have all substances and different plant families have a complex make up of secondary metabolites. Latex can be carcinogenic if rubbed continuously on body as can be smoking also. Avoid contact with plant saps which are oozing when plant is cut especially if its mikly oozing . Plants are fearing that someone want to eat them so they ooze out milky substances to ward off this danger. Animals dont like to eat some plants as this sticky latex is non palatable. Contact dermatitis could result if we contact some plants by hands. However all plants have some or the other qualities and chemicals good for human life. We have to search for them . Most of the present day medicines have their base in plants. Love plants , take care of them they will take care of you and your body. Choice is yours.