It would be an overstatement to say that this entire mess is "our fault", sure, but there is at least some responsibility the West has to accept for the way their Middle East policies have played out. In the first place the invasion of Iraq did leave behind a very unstable country with an effective power vacuum and surely there were better outcomes possible if more thought had gone into controlling the aftermath of Saddam's inevitable defeat. On the other side of the coin the non-intervention in Syria has had some consequences. I don't think arming what is now ISIS was ever on the cards but the situation there, left to its own devices, has evolved into something that is at least a three-side War as the Islamic militants can be regarded as separate from the Free Syrian Army, and both are fighting Assad and each other. An intervention there set up as a peacekeeping mission to force what was then both sides to come to the table might have allowed events to play out differently in a way that again stopped parts of Syria from becoming a power vacuum.
What is absolutely not the West's fault is the sort of group that has stepped in to fill this vacuum, and we shouldn't take any responsibility for the barbarous acts they are committing. But that we played some indirect part in the rise of ISIS/ Islamic State is unarguable, I'd have thought. It's probably important to acknowledge this because then the "it's our mess and we should play a significant role in justifying increased military involvement.