Fujitora didn't say he is going to protect the citizens without directly doing anything, he said he is going to protect the citizens by making sure Straw Hat Luffy doesn't go for Doflamingo's head, that is Fujitora's "justice" - stopping Luffy. The last chapter made that very clear, so Fuji isn't going to protect the citizens any other way except facing Luffy and stopping him from going after Mingo.