Boots on ground in Syria must be Arab ones
Even RAF commanders don't believe air strikes can defeat Isis. But the prospect of sending troops into Syria raises the spectre of coalition casualties - including members of the Irish Guards and Royal Irish Regiment. Have we learnt nothing from Iraq and Afghanistan?
As bombing continues in Syria and Iraq debate rages about the level of success it can achieve and whether it will lead to boots on the ground in Syria.
Concerns also grow about civilian casualties as Western and Russian aircraft hit their targets. Syrian aircraft are also striking targets where civilians may be killed or injured.
As politicians, journalists and academics argue for and against the bombing and protesters take to the streets, the emphasis remains on the question of civilian casualties and the effectiveness of bombing. Most discussions are shaded by recent history: Iraq in 2003, Afghanistan for more than a decade, Libya in 2011.
Many who march and protest against the bombing remember how Western nations went to war in Iraq in 2003 against a background of deceit by national leaders.
Common to both debaters and protesters is the question: what happens next?
No one - not even airmen - now believes that air power alone can deliver victory, whatever "victory" might be. Air power can certainly destroy infrastructure and claim lives. But it cannot win a war. Unless, that it, it is accompanied by action on land, those boots on the ground.
So, the common concern is that air strikes are but the first phase of a campaign that will draw in ground troops and, perhaps, lead to another prolonged engagement by Western powers - so-called "mission creep". That assumes those boots on the ground will be filled by Western feet. And that is a nightmare for all who remember too clearly the repatriation of dead servicemen and women through Royal Wootton Bassett and Lyneham.
Those dead included men of the Royal Irish Regiment and Irish Guards, and any future Western engagement in Syria could mean further casualties in either unit and among other Northern Irish personnel across all three services.
However, former head of the Army General Lord Dannatt has made clear that the feet filling such boots should not be Western. His reasoning reflects that of Professor Paul Moorcraft, an authority on the Middle East, who has spent much time in the region and knows some of the protagonists. In his view: "These are essentially Arab problems, so let them fix them. The West has tried - and failed."
He sees much of the regional turmoil as "the Muslim version of the wars of religion that nearly destroyed Europe in the 17th century".
Commenting that "it may be strategically sensible" for the West to avoid involvement, he notes that Western intervention has only made matters worse in the past.
Ideally, America especially, should stay out of a Muslim theological debate that began 14 centuries ago. However, Moorcraft adds that the availability of nuclear weapons, especially in Pakistan, means that "ethics and military strategy might compel the West to assume more than a watching brief".
There can be little doubt that the birth of Isis has made matters much worse. When Abu Bakr al-Baghdadi declared the new global caliphate on June 29, 2014, he claimed the allegiance of all Muslims. Al-Baghdadi, or Caliph Ibrahim to his followers, born near Samarra in Iraq in 1971, was a little-known imam when the invasion of Iraq occurred in 2003.
In the wake of that invasion al-Baghdadi was interned by the Americans at Camp Bucca. Although he wasn't seen as an advocate of violence, he appears to have had a catharsis in Camp Bucca, or simply because of the way the Americans were administering Iraq.
The end result is that the US authorities have placed a $10m bounty on his head and he has become a mystery figure known as the "Invisible Sheikh".
Ironically, the Americans released him after eight months (although some claim he was held for five years) since he was considered a very "low-level" threat.
He is said to have assumed a leadership role within Camp Bucca, although this surely would have come to the notice of his hosts.
Whatever happened, al-Baghdadi rose through a combination of determination, organisational skill and religious fervour to become the new caliph, proclaiming the birth of a new caliphate with authority - military, political and religious - over the Umma, the entire Muslim community across the world.
While most Muslims reject this claim, many support al-Baghdadi, seeing Isis as the beginning of this new worldwide caliphate. He claims it to be the only state that holds true to the Prophet's original ideals.
Although there are claims that al-Baghdadi was injured and perhaps paralysed in an air strike in March there is no proof of this, and he remains on the US Most Wanted list as a "designated global terrorist".
Abu Bakr al-Baghdadi holds to the belief that everyone in the world is a Muslim irrespective of their beliefs or lack of them. Thus all non-Muslims and all Shia Muslims (al-Baghdadi is a Sunni) are apostate and deserving of death unless they "revert" (ie return to Islam).
This belief is no more held by a majority of Muslims than is the belief within certain Christian denominations that only their adherents can enter Heaven.
What is the full extent of the threat? Al-Baghdadi and his followers want to rule the world to bring it under Sharia law. Their initial success in the Middle East has been blunted by air strikes, although the land they now control can be wrested from them only by military force.
There is no negotiating with Isis. This is an organisation and belief system that does not believe in negotiating. It will not have embassies nor employ envoys. All must come to it and be subservient.
It is difficult for many in the West, especially in Europe, to comprehend what Isis really means. And that's because so few in Western Europe today have any religious belief or even any understanding of religious belief.
They cannot understand truly how a set of beliefs could be perverted in such a way. They believe that there must always be a political answer.
To some extent David Cameron has understood, but the clearest appreciation of what Isis really is was expressed in the House of Commons last week not from the Government benches but from the Opposition. It was expressed by Hilary Benn MP: Isis is fascism, plain and simple.
As before, that fascism must be faced down. This time it must be faced down by Arab nations, supported where necessary by the West.
Those boots on the ground must be Arab, worn by Muslim soldiers. Otherwise the threat to the West will remain high as more radicalised young Muslim men and women flock to Caliph Ibrahim's call.
Richard Doherty was the editor of Professor Paul Moorcraft's book The Jihadist Threat: The Re-conquest Of The West? (Pen & Sword Military, £19.99)