Every generation has some product/ingredient that they didn’t know was dangerous at the time: tobacco, lead, asbestos, etc. What is that item for this generation?
Could be smart watches. Don't quote me on this, but wearing a watch 24/7 that emits light to constantly track your heart rate cannot exactly be good for your health (unless you truly need it)
Conversely, if smart watches with accurate health monitoring become cheap and commonplace it might drastically improve health outcomes by motivating people to see doctor's when needed for subtle heart issues that would otherwise go unchecked.