Oh, certainly. My point is not that they are harmless, or that their aims are noble(they aren't, and if they could they'd continue expanding until they ran out of room and/or infidels); but that this ideological commitment to territorial expansion also has downsides for them.
Since their desire is to expand(and their continued legitimacy as a 'caliphate' depends on it), they can expect basically all their neighbors to be frosty at best. The ones that aren't Real True Muslims can expect to have their heads sawed off and used to make snuff films, so they aren't going to be too happy, and will have a strong incentive to fight like their lives depend on it, because they do, and even the Real True Muslims can, at best, land an Emirate or similar subservient status. If the alternative is losing power entirely, they'll probably go for it; but they certainly won't like the idea. Aside from ensuring that local politics remain ugly, the enthusiasm for territory also requires a comparatively large amount of manpower dedicated to fighting relatively conventional battles for borders as well as doing boring but necessary administration and governance stuff. And, in addition to there being nothing quite like really, really, boring bureaucratic work to cool some hormonal, maladjusted 18-20something's zeal for Jihad, people fighting comparatively conventionally to take or hold territory are the type of army that we have the best shot at picking off from the air. They probably won't oblige us by behaving exactly like 1970s commies, only lower budget; but they aren't going to take and hold a contiguous nation-state without at least periods of relatively conventional warfare, of the kind the air force just smiles really wide when it looks down upon.
They can still be nasty fuckers, and they are; but their ability to focus on the 'far enemy' (ie. us) is pretty small compared to their ability to focus on the 'near enemy'(every last person who ended up on the wrong side of a nasty little tribal feud in the middle east). Not necessarily zero; but very low per unit manpower and resources.
Contrast to classic Al Qaeda, or the assorted islamist militants that Pakistan's ISI cultivates for use as proxies against India: such groups have no particular territorial ambitions, they just need some basic office and living space, they are generally at least somewhat willing to be 'ecumenical' about various internecine disputes as long as there are Americans and Jews and so on to attend to. Much less dramatic, in terms of capturing locations with actual place names and generally acting like a state; but much more flexible in their ability, and willingness, to deploy resources against soft targets wherever the opportunity arises, and much trickier to root out, since they both look much more like civilians and have a much better chance of having good relationships with at least one host country.
I would definitely agree that IS showing signs of actually expanding out of their little shithole would be Bad; but unless they can do that, their expansionist desires actually make them somewhat less risky to our interests because they'll be focused on slugging it out with their neighbors, rather than blowing up targets of opportunity worldwide. (Very, very, cynically, an IS that fails to expand might even have some benefits: if you want to remain even a nominally liberal democracy, you can't really do anything about religious wackjobs who hate you and your civilization; but live there anyway for some reason, until they actually do something criminal. If, suddenly, their most-likely-to-be-violent and/or most zealous people voluntarily start emigrating to some hellhole to get themselves killed, well, sucks for the neighbors; but some of your problems are now solving themselves.)
