When Texas neurologist Hamid Kadiwala told his parents he was heading to Gaza to volunteer at a hospital there, they begged him to reconsider. “Why would you take that risk?” they asked. What about his Fort Worth medical practice? His wife? His four children? But Kadiwala, 42, had been deeply shaken by images from Gaza of mass death and destruction and felt a responsibility to act. Israel’s siege on the small, densely populated Gaza Strip was “a history-shaking event,” Kadiwala said. “I want my kids to be able to say that their father was one of those who tried to...