Doing nothing is always an option. Sometimes it can even be a sensible policy. There is much to be said for modesty and restraint and an awareness that unforeseen consequences lurk around every corner. Even so, doing nothing has consequences too.
But the United Kingdom is not going to war in Iraq again. It is not going to war in Syria either. There are two parts to the battles against ISIS: an on-the-ground war and an in-the-air police action. We are, today's vote in the Commons permitting, taking part in the latter element of the battle. A punitive action designed to make it easier for those doing the real fighting - the Kurds and others - to prevail.
So let's not exaggerate the military significance of deploying half a dozen jets to hit ISIS. This is nothing like either Gulf War 1 or Gulf War 2. No-one is suggesting it should become anything like those conflicts either. No-one proposes sending 30,000 British personnel to the middle east. Even if we wanted to, we probably couldn't. Some perspective is necessary, please.
Aren't we, critics worry, doing precisely what ISIS wants us to do? Won't our involvement increase the risks this country faces? Blowback, anyone? Won't we, moreover, hand ISIS just the kind of propaganda coup they seek? Are we being sucker-punched here?
These are not daft concerns. Nevertheless, I am not sure they are persuasive. We must choose our own course, not grant ISIS an effective veto over our own decisions. Furthermore, we already face significant threats not all of which are over-hyped by the security services. And sometimes, you know, a fight can suit both sides. If we - that is, the international so-called community - do not confront ISIS now we may find ourselves regretting that failure at a later date when they have grown stronger and a confrontation can no longer be delayed - or denied.
We cannot talk to these people. There is nothing to talk to them about. That hitting them also benefits other parties for whom we have no great enthusiasm does not discredit the value or necessity of combatting ISIS.
But why us? Why not leave it to others? Well, in the first place, other countries are playing a part. Secondly, if there is a measure of collective responsibility in this action then it stands to reason that the United Kingdom should bear its part of that burden.
And thirdly, perhaps most pertinently, ISIS have made it abundantly clear that they consider us one of their many enemies. Their rhetoric confirms this; so do their actions.
No-one, I think, can accuse Her Majesty's Government of rushing to involve itself in this action. On the contrary, critics could make a decent case for arguing that Britain's response has been too slow - and too little.
What about the UN, critics caution? Well, what about it? Are we to grant Russia and China a veto over our foreign and security policy even as they decline to recognise or be checked by the UN themselves? This excessive respect for the UN is many things and abandoning our own ability to define our own national interest is one of those things.
It is another way of saying that if a band of murderous lunatics hellbent on jihad want to murder British citizens they may do so safe in the knowledge that the British state lacks the willpower to do anything about it. That's a kind of capitulation that sends a message too: Britain is no longer interested in defending its citizens or in avenging their murder.
Sometimes a problem really is a nail; sometimes you do actually have a hammer with which to address the problem. This, it seems to me, is one of those times.
ISIS are a scourge on humanity even, actually, a refutation of humanity. Their politics - if such it can be called - is a kind of super-murderous piracy. We have a choice between ignoring or confronting this abomination.
We cannot do it on our own but no-one suggests we can or should. But we can play a part and we should. Killing ISIS's brigands is not enough or the end of matters but it is, at least and at last, a start.