Abusive Online Groups and Relationships:
It's possible for people to be "brainwashed" over the internet. Text content on web pages can be presented in a way that invokes a suggestible state (like other written material can do, that's not an internet-only thing).
Sounds more like "persuasion" to me than a "suggestible state." If this is the case, then everything we read "brainwashes."
I think your redefinition of ideas and words could just as easily be called brainwashing.
A lot of it has to do with how savvy a user is. Cults that are into recruitment often use subterfuge and inexperienced internet users might not be alert to some of the worst tactics, such as using information gained through surveys to profile individuals and then ganging up on the individuals. Recruiters can pretend to have special insight or common interests and the target should be wary of them, just like in real life, where recruiters sometimes collect gossip before aapproaching a target and offering "help".