I've been following this debate for a long time, not wanting to get involved because I'm neither Jewish nor Muslim and because I think the NUS is pretty much an irrelevance to my life as a student. But I think it's worth adding a post because I think some people conflate things that aren't always the same.
There are four concepts that matter here:
1. Being against militant Zionism
2. Being against Zionism
3. Supporting terrorism
4. Denying or downplaying the Holocaust
The first of these is uncontroversial. Militant Zionists are those who settle lands not recognised by the international community as part of Israel. They are, in effect, stealing the Palestinians' homeland. This is clearly unacceptable to most people, including 99% of Jews, even most Israelis.
The second is a legitimate opinion, albeit one that flies in the face of international law and archeological evidence. Zionism is simply the belief that the state of Israel has the right to exist, with its borders as at 1967, on land inhabited by the Jewish people for at least 3000 years (archeologists have found the remains of synagogues dating back more than three millennia there).
The third, which Bouattia has done, is in my view absolutely out of order. She has called for 'armed resistance' by Palestinians and refused to condemn ISIS. If one student is emboldened by her actions to join ISIS or give money to a terrorist group, she should be held responsible for her contribution to the resulting deaths.
The fourth thing she hasn't done so far as I'm aware, but someone else did it and hasn't been condemned. It's a small step from 'there's nothing unique about the Holocaust - we should focus more on other atrocities, despite the fact that they killed a tiny fraction of the number of people' to 'there's a Jewish conspiracy in the media and academia to overstate the significance of the Holocaust' or even 'those pesky Jews made it all up.'
Though I'm not Jewish, my girlfriend is, and it's an unspoken understanding between us that we'll get engaged this summer when she finishes her degree and married two years later when I complete mine. As with most Jews, family is very important to her and I've met most of her extended family. You need go back only two generations to find grandparents who grew up as orphans or in poverty and suffered huge losses of close relations because of the Pogrom. Her parents and grandparents have family keepsakes representing people who died through overwork in the ghettoes, of starvation or disease on forced migrations or in the gas chambers. And a couple of generations earlier, something similar happened with the expulsion of Jews from the Russian countryside. Some moved to the US or UK, but many moved to Poland and other parts of Europe where their descendants were persecuted again when Hitler came to power.
Given this history, I don't think it's surprising that it's really important to most Jews that the full horror of the Holocaust is recognised and that the world preserves the right of Israel to exist. Even if most never visit it, let alone live there, they want to know it exists as a place of last refuge if things get really bad. And when Muslim terrorists targeted Jews in Paris recently, some Parisian Jews relocated to Israel, as is every Jew's birthright.
Hearing anyone, especially someone with power and influence among students and Muslims, challenging Zionism, supporting those who commit terrorist acts against Israeli Jews and refusing to condemn ISIS or a motion opposing the marking of Holocaust Memorial Day, is deeply offensive to most Jews, as well as people like me who love Jewish people. My girlfriend is an amazing person and her family are some of the warmest, most welcoming and most generous people I've been privileged to meet, in part because of their faith and the amazing culture they've grown up in. Ms Bouattia's infantile posturings offend and frighten them. It's not clever or funny, and she should not be in the position she holds.