People are not (just) upset that Beverly died.
People are upset that Fuller admitted that the plan from day one was to kill her. That she was a character designed to die. That he developed her precisely to make her death hurt.
People are upset that she’s going to be hacked up and put on display - something that Miriam Lass or Abigail Hobbs were not subjected to.
People are upset that the writing surrounding her death was forced and contrived. That Beverly, a methodical, pragmatic, level-headed field agent, would break into Hannibal’s house to obtain illegal evidence that she couldn’t use to exonerate Will. That Beverly, who’s been demonstrated on more than one occasion to be a terrific shot, didn’t manage to shoot Hannibal before he lunged for the light switch.
People are upset that all of this happened to the most developed woman of color on the show.
People are upset that the only other woman of color on the show is currently dying (and that within the same episode, that woman’s choice to die was removed from her).
People are upset that Fuller, and a good chunk of the fandom, doesn’t see anything wrong with this.
It’s not just about Beverly. But it’s completely about Beverly.