Since Amazon seems to be specifically targeting parents with this ad, we might as well also mention that children will certainly find the Dash amusing with its beeping and red lights, and if Amazon automatically ordered everything your kid scanned for personal amusement, they'd have a lot of angry customers.
EDIT: On second watch, the ad does say "you can check out on Amazon Fresh or a smart phone", so they've explicitly indicated that there will be a confirmation process before the order is placed. This is just meant to make it quick to collect your list instead of having to type in "chocolate chips" and scroll through hundreds to find the brand you like and then repeat for every item in pantry.