In broad strokes, I doubt that most of us who have posted in this thread are too far apart when it comes to how we feel about the ISILs and Boko Harams of the world.
In purely pragmatic terms, I don't think that ISIL, or al-Qaeda, is an existential threat to either the US or to the liberal democracies of the world (Israel being an exception, if a convoluted one). As others have suggested, it'll take "them" a long while to behead everyone on their ****list. To thethe and some others: I think you have a legitimate blind spot when you discuss these issues. Although a lot of horrific things have happened in European countries with large and disaffected Muslim minorities, most of the turmoil wreaked by violent jihadists or islamic extremists has happened in places where there is widespread disconnection and/or power vacuums owing to either old-school colonialism or contemporary neo-colonialist policies. I think that you should at least acknowledge this context, and the fact that violence motivated by religion is one of the most predictable things to emerge from such situations. In Rwanda it was purely ethnic. In the Balkans it was ethnic, with religion sort of half-heartedly grafted on top. In today's Nigeria, it's religious, in the the Levant it's both sectarian and religious . . . with the political, as always, lurking behind the scenes. Boiling it down to an essential religious or even ideological war seems to me to playing into the hands of the putative enemy.
I don't think that the strategic missteps of the past should cause up to throw up our hands and do nothing. I don't think that we should talk about chickens coming home to roost or glass houses, and expect that to be the end of the conversation. But I also think that we should be clear-eyed about some things. ISIL is the sum of our last 10-12 years of middle east policy. The prominence of the Salafi jihadist school of thought is a direct result of Western intervention in the Hejaz region. We--the US and the Brits--elevated those weirdos to power in the gulf, with their retrograde religious thoughts in tow, and kept the money faucet flowing while they bribed their imams to keep the jihad outside their borders because we wanted cheap fossil fuels. It's complex, but it's also exactly that ****ing simple.
That in itself isn't a reason to do nothing, or to make excuses, or to tolerate savagery. I admire the appeals to the best parts of our nature, no matter what political quarter they emanate from. I think it's worthwhile for all of us to examine our own values and beliefs and how we go about creating the world that our kids and grandkids will live in. We should be damned cautious and thoughtful about how we approach confronting the issue, but we should confront it.