Ali Harbi Ali’s explanation for killing David Amess is not only icily matter-of-fact but highly inconvenient. Ali, recently convicted in the Old Bailey, says he was motivated by the Southend West MP’s vote for airstrikes in Syria. The accused told the jury of his regret at being unable to travel there, adding: “I thought if I couldn’t go join Islamic State, I should try and do something here to help Muslims here.”

Amess’s membership of Conservative Friends of Israel was another “big problem” for Ali, and he also described a plan to “attack and hopefully kill Michael Gove”. During cross-examination, the 26-year-old said he felt no shame, stating: “If I thought I did anything wrong, I wouldn’t have done it.” Asked what the MP’s death had achieved, Ali replied: “For one, he can’t vote again.”

Francois was feeding the roaring furnace of a moral panic

Statements like these are no doubt why a jury at the Old Bailey took only 18 minutes to convict him yesterday afternoon. They are also inconvenient because they cast fresh and particularly unforgiving light on how David Amess’s colleagues responded to his death. Social media was identified as the culprit with a lockstep uniformity common to the British political class and a North Korean military parade.

Home Secretary Priti Patel promised “big changes” to the law and pledged to “look at everything”, including a ban on online anonymity. Digital, Culture, Media and Sport Secretary Nadine Dorries admitted her Online Safety Bill “might not have changed what happened last week” but said Amess’s death had “highlighted” the internet as “the home of disgusting, often anonymous abuse, and a place where people are radicalised”.

Sir Keir Starmer urged the Prime Minister to “build on the desire shown by this House… to get things done and commit to bring forward the Second Reading of the Online Safety Bill”, while Speaker Lindsay Hoyle called on social media companies to “get their act together”, saying: “If it was up to me and I was in charge of legislation, I would have done something.”

It was a total inversion of the ground rules established after the murder of Jo Cox, which held that the killer’s motives must be confronted and debated promptly, and censured anyone raising other potential causes. Now the motives were secondary, if even that, and censure was reserved for those questioning the relevance of Twitter trolling to the killing of an MP.

The most egregious effort came from Mark Francois. When MPs gathered to pay tribute to their fallen colleague, Francois’s speech was by far the best received. After some personal reflections, he complained that MPs “came here to try to help people” and “for this, we are now systematically vilified day after day”. “Enough was enough,” he declared, adding:

“I humbly suggest that we get on and do some legislating. I suggest that if we want to ensure that our colleague did not die in vain, we all collectively pick up the baton, regardless of party, and take the forthcoming Online Safety Bill and toughen it up markedly.”

Francois called his proposal “David’s Law” and said it would provide that “while people in public life must remain open to legitimate criticism, they could no longer be vilified or their families subjected to the most horrendous abuse, especially from people who hide behind a cloak of anonymity”. The legislation would also cover Facebook comments suggesting council planning decisions had been “a brown envelope job” and online vilification of GPs and their receptionists.

No doubt Francois was speaking from grief, but he was proposing a sweeping legislative clampdown on speech, not on the basis of threat or incitement to violence but “vilification”. He was, in effect, proposing a hate speech law in which employment as a politician (or a GP or a receptionist) would be a protected characteristic.

More to the point, Francois was feeding the roaring furnace of a moral panic. Without a skerrick of evidence that social media had anything to do with David Amess’s death, Francois and the rest proposed drastic legislation to punish members of the public for being nasty to MPs on Twitter. No one would gainsay that some MPs face foul abuse online — female, Jewish and black MPs in particular — but where such foulness crosses into criminality, the law already provides remedies.

Our sympathy for the turmoils of mourning can only go so far. Ministers and MPs overreacted but they overreacted in a cynical, self-serving way, hitching onto the killing of their colleague a pre-existing grievance, one unconnected to his death. There was raw emotion at work but there was also cold opportunism.

Islamism has not stopped gunning for Britain

There was cowardice, too. Talking about Twitter abuse meant not having to talk about the facts of the incident, facts already widely available but which sketched out an unwelcome offender profile and possible motive. Within 12 hours of the attack, we knew that it was being treated as a terrorist incident, that the initial police investigation had revealed “a potential motivation linked to Islamist extremism”, and that the British Somali suspect had previously been referred to the Prevent counter-radicalisation programme.

Far more clear-sighted than MPs were the mosques of Southend, which released a joint statement within 24 hours denouncing “an indefensible atrocity” that was “committed in the name of blind hatred” and urged that “the perpetrator be swiftly brought to justice”.

A British-born Muslim has told a court that he stabbed an MP to death because he voted for airstrikes against Syria. The worldview he has outlined to the court confirms a grim landmark, albeit one most of the political class would prefer to ignore: David Amess was the first British MP killed by Islamism.

There will have to be a new conversation. It will have to address the ongoing appeal of Islamism to British-born Muslims; the impact, if any, this should have on immigration and asylum policies; the failure of existing counter-extremism strategies and what to replace them with; and the way we police Islamist terrorism. Islamism has not stopped gunning for Britain because we have stopped acknowledging it or prefer to pretend it is something else. It remains a threat not only to human life and national security but to integration, cultural cohesion and the free society which the British inherit as their way of life.

We must have that conversation, however awkward, not only because our safety and our lives depend on it, but our dignity, too. Islamist supremacism lies at the heart of the enemy’s doctrine, which is what leads him to kill MPs in Christian churches or blow up teenagers at pop concerts or ravage commuters on the Piccadilly line. His brazenness, however, he gets from us and our weak, dishonest response to his every outrage, which only spurs him to greater outrages.

A conversation like this requires courage and candour, neither of which are much in evidence among a political class that sees one of its own slain and would rather talk about trolling than terrorism.