Lol, I keep explaining to you that it was strictly an issue about optics. The citizens were threatened by seeing the Birdcage close in on them. If Fuji stops it then they will feel saved by the marines, and will also question why Fuji just doesn’t help end Doffy. He didn’t want to give the marines any credit, it’s all calculated. If the people were actually gonna die, then Fuji will step in. This just means that he knows that nobody was actually gonna get harmed, he can sense everybody on the island.