I think their point is that a lot of us, upon hearing "group A tend to exhibit more of some negative trait X than some other group B" mentally start to associat

I think their point is that a lot of us, upon hearing "group A tend to exhibit more of some negative trait X than some other group B" mentally start to associate A with X and this creates a social stigma - just because how our brains work. I wish there'd be some way to phrase such statements in a nonjudgmental way, without introducing a perception bias...