As you said, this unified caliphate would be fundamentalist or, at the very least, "non-liberal."
I didn't say it would be fundamentalist; the caliphates of the middle ages certainly weren't. ISIS and AQAP are fundamentalist. Do you think fundamentalist Christians are good examples of Christianity? If a large portion of Europe or America coalesced into an explicitly theocratic political body, do you think it would be "fundamentalist"? I don't.
But it would definitely be "non-liberal", since liberalism is strain of Christianity and we're talking about Islam here.
What gives you any confidence that means the jihad is not just for a unified caliphate, but for a global caliphate.
I'm not suggesting that we empower ISIS, AQAP, or any other jihadist group. I'm suggesting we might be better off encouraging MENA to coalesce into a stable unified theocracy.
I don't know why you have this confidence that the unified theocracy would be content to "live out the tenets of their faith in peace," even if fundamentalism were allowed to reign within their borders.
I don't think such a caliphate would be fundamentalist; only authentically Islamic. Though you seem to be conflating those two terms. Regardless, the medieval caliphates are a good example.
You're probably right that we won't be able to win them over via mass conversion, but they don't share your sentiment.
Christians have the
Great Commission, but we also believe that secular and temporal power should be separated. Muslims also believe they have a duty to convert the world, but since Islam is inherently political, they're OK with "evangelizing" in ways that Christians find abhorrent. That's a great reason for maintaining healthy boundaries with such a caliphate (if one ever forms), but it's not a good reason for continuing to sow discord across MENA, because the
status quo poses dangers that aren't so easily contained.
The want the whole world under their banner and their evangelization methods are a bit more explosive than ours.
If you want to look at this strictly from the angle of
realpolitik, it would be a
lot easier for us to deal with/ contain a unified caliphate through diplomacy, treaties, etc. than it will be to preserve our civil liberties through waves of terrorist attacks and an onslaught of refugees.