It could be a valid point to bring up, but being combative/aggressive with it doesn't benefit the conversation. You could word it as something "perhaps some people need to question if something is a bad habit, or if they are addicted...", rather than calling parent 'ridiculously naive'
> Person 1: Just stop it. Want harder.
> Person 2: I can't.
> Person 1: Well, you have an addiction then, not just a bad habit; my point was about habits.
If we grant this: then the great-grandparent's response fails to inform us of anything beyond merely how we choose to define words. The advice works until it doesn't, which is tautologically true but not useful.
I took the original comment as question if you actually want the habit or are just doing it out of social or self pressure, or just for the sake of 'that seems like a good thing'.
Emphasising that you are free to drop habits, rather than pressuring yourself to achieve something that you might not really want.