A person can be reasonably confident that their immediate sale of an item is going to go to someone who will use it responsibly... while still worrying about it

A person can be reasonably confident that their immediate sale of an item is going to go to someone who will use it responsibly... while still worrying about its disposition five or ten years down the line. (Microsoft has already let this problem sit for 26 years, after all.) That still doesn't mean the person has any particular legal or moral responsibility to monitor their original customer indefinitely just because there's a future risk.