Last weekend, hundreds of thousands of men, women and children around the world marched to express their disgust at Israel’s air and ground assault on the Gaza Strip, and among them were swathes of Jews and Israelis. This is one of the few situations in which it makes a difference to stand up and say: not in our name. Not now, not ever again. Being Jewish, or having Jewish roots, doesn’t make you responsible for what is happening in Gaza, but it does mean that your dissent carries that much more weight.