Agree that is a big-time longer-term threat but "user won't know the difference" means the user gets the order with parity in delivery time, product quality, returns experience, etc...that won't be replicated overnight, at least not at scale (interesting to think what products could be done first...similar to Amazon starting with books).
Meanwhile ads made Amazon $19.8 billion last quarter alone, even while detracting from our user experience. Can't rip that business away overnight either, but it is less of a lift imo.