I can’t argue with him. They will conquer lots of places if someone doesn’t wipe them all out.
Sorry, but whilst ISIS is unusually competent and well armed for a bunch of ululating middle eastern savages, they cannot conquer territory anywhere where there is a contiguous non-Muslim majority. In relative terms, they will remain nothing more than a nuisance.
The Nazi threat was only confronted and destroyed when they started invading and conquering other European countries and subduing them. Until ISIS is capable of invading and conquering a neighbouring non-muslim country, there will never be taken seriously enough to inspire the west to launch a full-blown WWII style war of annihilation where the enemy will either surrender or die. They will simply remain a festering sore for decades to come, because bad as they are, few people will consider price of destroying them worth the necessary sacrifice to do so.