I've never heard somebody say that Triceratops' horns were used exclusively for display. However it is very likely that ceratopsians evolved these weapons for fighting each other and not for fighting predators (this doesn't mean that Triceratops wouldn't have used their horns to protect themselves from predators)
I always thought the hypothesis that the horns were exclusively ornamental was ridiculous. Like, they're practically aimed at t. rex's stomach
There are T. rex skeletons with horn marks in them!
I've never heard somebody say that Triceratops' horns were used exclusively for display. However it is very likely that ceratopsians evolved these weapons for fighting each other and not for fighting predators (this doesn't mean that Triceratops wouldn't have used their horns to protect themselves from predators)