(Note that I'm only talking about messages that cross the line into legally actionable defamation, threats, etc. I don't mean anything that's merely rude or unpleasant.)
But as you pointed, not everything has legal liability. Socially, no, they should face worse consequences. Deciding to let an AI talk for you is malicious carelessness.
This is quite ironic since the entire issue here is how the AI attempted to abuse and shame people.