STPs believe that the best way to protect others is to help them become more self-sufficient and thus self-protective. STPs are not and will never be caretakers. ISFJs on the other hand can and should learn to establish boundaries. Nevertheless, many ISFJs do take great pleasure in being needed.
However, if there is some real physical or material harm occurring, the STP should be confronted directly and all steps should be taken to stop any such harm.