It was a self-destructive (career-destructive?) act. During the rehearsals she held up a different photo, one of a Brazilian boy who had been killed by police, and didn’t tear it up. That was what the show’s cast, writers, and producers expected. She deceived the show to make her statement and Lorne Michaels took that as a betrayal. However strongly she felt about the issue, it was unprofessional to use SNL as her platform for shock value. That was what she was banned for. I don’t know what she thought would happen or if she even considered it, it was that important to her. It was certainly a memorable moment from the 90s.