I've learned that it's best not to say anything about a terrorist atrocity on social media, especially not if it confirms one's political prejudices. It just looks crass, or it has when I've done it. Try not to say anything profound either, as it will probably look insipid; also ideally do not make any point about similar atrocities occurring in less well known parts of the world, as people will quite reasonably think you're just scoring points. And best not to bother with the tweets of solidarity, which are superfluous these days surely; France and Belgium and Germany are our close allies, friends and neighbours, and it goes without saying that when one of us is attacked we feel for them.

German social media is apparently filled with anger, not with Islamic extremists or Angela Merkel but with Alternative für Deutschland and its supporters. I'm not sure what the psychological condition is called; I suppose it's a form of Stockholm Syndrome.

I can understand the human urge to protect the vulnerable, refugees and Muslims generally, from hostility as these awful events repeat themselves. It's easy to sneer at politicians who come out with vapid theological comments, as I have in the past, but their job is to protect all the country's citizens. I can also see why this urge might convince an intelligent person that Merkel's migration policy has actually helped the fight against terrorism. But it's extremely unlikely; all things being equal, hosting refugees does lead to an increase in terrorism, although the risk is smaller in richer countries, largely because they have better security services. It's at times like this when I thank God for ours, who have saved countless lives in our country by preventing a good dozen attempts at mass murder. I'd suggest we all send them Christmas presents but I imagine they'd be destroyed. But if you're reading - thank you all.

In fact, Merkel's policies have some pretty serious implications for Germany in the future. I've read many people arguing that it was actually a clever, shrewd policy to admit one million migrants because Germany has a low birth rate and needs more people. Yet the education levels and skill sets of most of the people who have entered in the past 18 months are, by German standards, extremely low; Germany has a fairly high-wage economy, especially compared to Britain, and there are not a whole lot of positions available for low-skilled men. The number of recent migrants who have found employment is exceptionally low. Employment rates among second generations migrants from the Middle East, mostly Turkish, are also considerably worse than ethnic Germans.

On top of this, we need to look at what technology is coming our way: in the next ten years, for example, automated cars are going to be putting hundreds of thousands of men out of work just in Britain. All the Uber drivers I've spoken to have come from the Muslim world; all have been hardworking, courteous and obviously doing their best by their family; unlike me, they've made the effort to move country and have to put up with boring drunks like myself talking to them. But the low-skilled jobs they are currently doing are not going to exist for that long, and many of their sons will grow up with workless fathers, feeling confused about their identity in a rootless world, at far higher risk of mental illness, struggling to find work themselves, and feeling neither fully part of this country nor that of their father's. In these circumstances an internationalist ideology rooted in a sense of brotherhood and rage at the rich, decadent, western world is going to appear hugely attractive.

Because posterity is a concept that does not feature strongly in democratic politics an overwhelming aspect of the migration issue is ignored, that the real problems do not arise with the hard-working immigrants doing the nightshifts but with their sons who, contrary to what the likes of the LBC host James O'Brien hopes, will not thank Germany for their situation.

But people react badly to these sorts of arguments, which is perhaps understandable. Ah, they'll tell you, we're far more likely to be killed in car crashes or by baths or in freak accidents. Of course we are, but none of these everyday tragic causes of death - all of which are in continual decline - have the same corrosive social effect as does having a section of the population out to kill the rest of us.

I was in France this summer, which almost reminded me of visiting Northern Ireland as a kid; even in a village wine festival I counted three armed policemen and four soldiers with machine guns. Increasingly in England, too, there are heavily-armed police not just at railway stations but at religious sites; there is likely now to be more and more security at every event where large numbers of people gather. In Sadiq Khan's words, such things are just 'part and parcel' of everyday city life, but they're a very costly part of it and one that has a far larger impact than the relatively small death toll involved.