Because there's only one person who could have convinced FCG so utterly that they weren't a "person" or "alive", and that's Dancer. Which means she was very unlikely to have recognized FCG as a living being like Joe. She's also been shown to be emotionally manipulative and has no compunction using people, with her "Ex". There was also the "Party Stress Doll" discussion earlier in the episode, when as far as we know Dancer's party only comprised herself, FCG, and 4-5 mindless automatons she built. Now, the other bots didn't need a Stress Doll, FCG wouldn't use a Stress Doll, and why would Dancer need a separate one when she had 5 perfectly good ones around her. Let alone who seems compelled to offer themselves up for that sort of abuse.

Outside of that. Red-Mode was triggered by an emotional catalyst that hurt FCG. And outside of Chetney (so far) his verbal attacks on both Fearne and Laudna resonated with emotional issues/stresses FCG had been dealing with for quite a while. Parental Abandonment in the case of Fearne, which FCG has been struggling with since learning Dancer was alive; but never came back. And "Never being alive" to Laudna, when FCG is the one who insists the most that they aren't alive. And argues against the contrary.