New Zealand has declared it illegal to possess a copy of the Christchurch terrorist's manifesto.
The manifesto reportedly calls for mass murder. (I've got better things to do than read it. Smells like shit, why taste it?) To make it a crime to call for murder is proper; the only issue is where to draw the line.
However, laws prohibiting the possession of a copy of a publication—no matter which publication—violate basic human rights. In addition, they create an excuse for dangerous massive surveillance, as well as dangerous searches of individuals' libraries. Even if you don't have a copy, you might be investigated based on the suspicion you have one. This offers the state an excuse for a fishing expedition against any chosen target. We must get rid of such laws.
For the long term, I feel more endangered by laws authorizing censorship than by right-wing fanatics. A fanatic with a military-style high-velocity semiautomatic rifle is dangerous. A soldier armed with a military high-velocity automatic rifle is even more dangerous. Likewise cops with large-magazine semiautomatic pistols; you can run away and hide from a fanatical shooter for the necessary period of time, but it is nearly impossible to hide from cops for the rest of your life.
The fanatic is dangerous due to an ideology of hate. The soldier or cop doesn't even need an ideology of hate to endanger people—orders are often sufficient. For where this can lead, consider the Tibetans and Uighurs in China, and everyone else in China for that matter. And the "security" forces sometimes bring an ideology of hate to the job. For recent examples, consider the Rohingya in Burma and the Kurds in Turkey. (Recall that Erdoğan launched a military repression campaign against the Kurds so he could play a hate card for the next election.)
Thus, even though we want the state to work to protect us from fanatics, as well as many other jobs (see here), we must never accept that as an excuse to weaken human rights protections that stop the state from using that power to tyrannize us.