Tapioca and and pectin are added to yogurt as a thickener. They are not particularly bad for you. They are unnecessary, and they are not added to the better quality yogurts. They are a cheap way to achieve consistency in the product, rather than using high quality controls in the process of making the yogurt. Properly made yogurt, without tapioca and pectin, can be just as thick as yogurts made using those additives.
Tapioca is a starch extracted from manioc, or cassava root. Much like arrowroot, it is used as a thickener. While they are considered easy to digest, both have very little nutritional value. Tapioca is a staple food in some regions and is used worldwide as a thickening agent in various foods. It is considered a gluten-free food
Pectin is produced commercially as a white to light brown powder, mainly extracted from citrus fruits, and is used in food as a gelling agent particularly in jams and jellies. It is also used in fillings, medicines, sweets, as a stabilizer in fruit juices and milk drinks, and as a source of dietary fiber.