I don't think "zero tolerance" is an accurate reflection of what happened in 1970. I believe there were protests in several cities after the Act was invoked.
Here's one from Toronto on October 17th, 1970.
Things were a bit more repressive in Quebec, but it was also an internal crisis. I don't think the Israeli government honestly believes that people protesting in Israel are actually working with Hamas.
Granted, it's pretty easy to understand why Israelis and their government might feel the way they do given what they've gone through. But significant curtailment of civil liberties and letting feelings of retribution guide your policy rarely works out in the long term. There's a reason why it's a credible theory that Hamas did this basically in order to suck Israel into a damaging quagmire and to push both sides to the extremes, and that's because it's a real thing that happens. And to some extent, Israel is falling into that trap.