Then any media service which lets a user deliver a message enables gaslighting. HN is a gaslighting service because it allowed you to deliver denigrating content to me.

No, gaslighting is systematically disorienting a person by staging confusing events, and blaming that confusion on the target themself. A one-way pipeline of targeted ads is not gaslighting, unless you call your wife crazy when she complains about all these weird ads she's seeing. But that's not what this service is automating.