The recent rash of attacks in the West by terrorists, beginning in Nice and most recently occurring (dare I say ending?) in Saint-Éttiene-du-Rouvray, have injected a great deal of tension into political debates over multiculturalism, immigration policy, and domestic security. Some people have begun speaking of a "war" between Islamism and civilisation. These worries are not unfounded, but nor are they in proportion with those which a rational observer of the facts would entertain.
First, let's remark on the generally petty level of the violence involved. Today's attack killed one person and left another fighting for life. Sunday's bombing in Ansbach injured fifteen, but killed no-one. Nine people died in the shooting in Munich last Friday. The attack in Nice, of course, killed 81 innocents, but such attacks are rare, coming perhaps two or three times a year at their most frequent. These numbers perhaps sound bad in the abstract, but let's make some comparisons. Each year in the UK, which has the second safest roads in the world, more than 1700 people die in traffic accidents. (That itself is a massive improvement on the past: 2006 was the first year since records began, 80 years previously, that the figure was under 3000). If we can absorb 2000 deaths from traffic accidents every year, I think we can similarly absorb a couple of hundred deaths from terrorism.
Second, we could prevent most terrorist violence if we really wanted to. With the (admittedly large) exception of the Nice attack, every perpetrator of a notable terrorist attack in the West has been known to domestic intelligence (example). Why aren't the attacks stopped, then? Because doing so would mean arresting people based on suspicion that they might commit a crime, rather than evidence that they had already done so. We could stop most terrorist attacks, but this would come at a cost in civil liberties.
I don't want to say that such costs should never be paid. Going back to the traffic example, we don't ban people from driving in order to prevent traffic accidents - but we do require them to wear seatbelts. There may well be low-hanging fruit to be had: policies that will, with minimal expense or inconvenience, reduce the incidence of terrorism upon our societies (note: preventing thousands of people from entering the country they want to live in does not count as "minimal inconvenience").
At the same time, though, we should note the possibility that we have already gone too far down this route. Airport security, for example, incurs vast costs in time for gains in security which are small to non-existent, and of dubious necessity: air travel is in fact considerably safer than road travel.
Laying my cards on the table: I think we should basically just ignore terrorism. (In the first world, that is: in the Middle East it's actually a very serious problem, although what that means for our politics I don't know). It is genuinely possible that there exist low-hanging-fruit policies which we ought to implement - mandatory detention of people returning from ISIS is very plausibly one, along with state attempts to promote moderate Islam and perhaps even some censorship of violently Islamist views (although my liberal side is very worried by this last idea). But understand that there are no two ways about it: if this becomes a war, Islamism will get curb-stomped.