We could let them have Iraq and Syria, which are war-torn basket cases anyway, but that wouldn't satisfy them. The caliphate is just a step towards the overarching goal of imposing their ideology on all of us. The means of achieving that is a global war between Muslims and non-Muslims.
Thus, as has been pointed out, Trump's anti-Muslim demagoguery plays into Isis' hands: in tone and content his outbursts reinforce the Isis narrative that Muslims and non-Muslims are mutually incompatible and therefore on a collision course.
Deep down Trump may know or suspect this but, being an egomaniac - if not a megalomaniac - who believes the end justifies the means, he has no qualms about inciting fear and loathing of Muslims and pandering to America's considerable reserves of paranoia.
So Trump goes up in the polls, his supporters are reassured that someone's taking their concerns seriously and Isis' strategy is working.
While Trump - narrow, short-term political considerations aside - can't see the wood for the trees, some of the criticism of him is equally short-sighted.
Apart from being overblown, the Hitler comparisons miss the point because they ascribe Trump's appeal to his personality and showmanship. There's obviously an element of that but those gravitating to Trump are doing so because they believe he gets it. He understands what keeps them awake at night.
And they're not alone. The race for the Republican presidential nomination still has a long way to go and many commentators still expect, albeit with less conviction than a couple of months ago, that Trump will fizzle out like a skyrocket, but this weekend France holds the second round of its regional elections.
If the results of the first round are replicated, Marine Le Pen's far-right Front National will assume control of three of France's biggest regions with a combined population of 16 million.
This is old-world, sophisticated France, a nation deeply scarred by 20th century extremism, not insular America.
One thing that particularly fires up FN and Trump supporters - and which Le Pen and Trump are adept at exploiting - is the perception that opposing immigration or dwelling on the religious affiliations of terrorists will be shouted down as racist.
The problem with the self-evident truth that the vast majority of Muslims are not terrorists or terrorist sympathisers is the movement across the divide. Syed Farook, the male San Bernardino shooter, was an American-born and -raised, mild-mannered, model citizen one day, a jihadist the next. Isis and similar groups are exerting a mysterious gravitational pull on young people in Muslim communities the world over, ours included.
The situation is too serious to be inflamed by demagoguery and the debate too important to be constrained by self-appointed thought police.
Ultimately, jihadism is a Muslim problem requiring a Muslim solution, both on the part of Muslim communities in the West and the Muslim countries surrounding the terrorist epicentre. We are on the same side and they have as much if not more to lose than we do.
